Electrolyte and secondary battery

ABSTRACT

Secondary batteries capable of improving cycle characteristics are provided. The secondary battery includes a cathode, an anode, and an electrolytic solution. A separator provided between the cathode and the anode is impregnated with the electrolytic solution. The electrolytic solution contains a solvent and an electrolyte salt. The solvent contains a cyclic compound having a disulfonic acid anhydride group (—S(═O) 2 —O—S(═O) 2 —) and at least one of a nitrile compound. Compared to a case that the solvent does not contain both the cyclic compound having the disulfonic acid anhydride group and succinonitrile or a case that that the solvent contains at least one thereof, chemical stability of the electrolytic solution is improved. Thus, even if charge and discharge are repeated, electrolytic solution decomposition is inhibited.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.13/258,109, filed on Sep. 21, 2011, which is a national stage ofInternational Application No. PCT/JP2010/054634 filed on Mar. 18, 2010,which claims priority to Japanese Patent Application No. 2009-073661filed on Mar. 25, 2009, the disclosures of each of which areincorporated herein by reference.

BACKGROUND

The present invention relates to an electrolyte containing a solvent andan electrolyte salt and a secondary battery using the same.

In recent years, portable electronic devices such as combinationcameras, digital still cameras, mobile phones, and notebook personalcomputers have been widely used, and it is strongly demanded to reducetheir size and weight and to achieve their long life. Accordingly, as apower source for the portable electronic devices, a battery, inparticular a small and light-weight secondary batter capable ofproviding a high energy density has been developed.

Specially, a lithium ion secondary battery using insertion andextraction of lithium ions for charge and discharge reaction, a lithiummetal secondary battery using precipitation and dissolution of lithiummetal and the like are extremely prospective, since such secondarybatteries are able to provide a higher energy density compared to a leadbattery and a nickel cadmium battery.

As an electrolyte of the lithium ion secondary battery and the lithiummetal secondary battery, combination of an ester carbonate solvent suchas ethylene carbonate and diethyl carbonate and an electrolyte salt suchas lithium hexafluorophosphate is widely used, since such a combinationhas high electric conductivity and stable potential.

In addition, regarding electrolytic solution composition, varioustechniques have been proposed for the purpose of improving batterycharacteristics such as cycle characteristics and storagecharacteristics. Specifically, in order to improve cycle characteristicsand storage characteristics, a disulfonic acid anhydride (refer toPatent documents 1 to 3), a nitrile compound (refer to Patent document4), a diisocyanate compound (refer to Patent document 5) and the likeare used. Further, in order to improve swollenness characteristics, afluorinated ether compound and the like are used (refer to Patentdocument 6). In addition, a dicarboxylic anhydride such as a succinicanhydride (refer to Patent document 7), sultone, a pyrrolidone compound(refer to Patent documents 1 and 2) and the like are used.

CITATION LIST Patent Documents

-   Patent document 1: Japanese Unexamined Patent Application    Publication No. 2004-022336-   Patent document 2: Japanese Unexamined Patent Application    Publication No. 2004-281368-   Patent document 3: Japanese Unexamined Patent Application    Publication No. 2008-098053-   Patent document 4: Japanese Unexamined Patent Application    Publication No. 2005-072003-   Patent document 5: Japanese Unexamined Patent Application    Publication No. 2007-242411-   Patent document 6: Japanese Unexamined Patent Application    Publication No. 2002-343424-   Patent document 7: Japanese Unexamined Patent Application    Publication No. 2000-268859

SUMMARY

In these years, high performance and multi functions of the portableelectronic devices are increasingly developed, and the electric powerconsumption thereof tends to be increased. Thus, charge and discharge ofthe secondary battery used as a power source are frequently repeated,and the cycle characteristics tend to be lowered. Accordingly, furtherimprovement of the cycle characteristics of the secondary battery hasbeen aspired.

In view of the foregoing problem, it is an object of the presentinvention to provide an electrolyte capable of improving cyclecharacteristics and a secondary battery using the same.

An electrolyte according to an embodiment of the present inventioncontains a solvent and an electrolyte salt. The solvent contains atleast one type of sulfone compounds expressed by Formula (1) and Formula(2) and at least one of a nitrile compound and compounds expressed byFormula (3) to Formula (4). A secondary battery of the present inventionincludes a cathode, an anode, and an electrolyte containing a solventand an electrolyte salt, in which the electrolyte has the foregoingcomposition.

-   (R1 is an alkylene group with carbon number from 2 to 4 both    inclusive or a halogenated group thereof, an alkenylene group with    carbon number from 2 to 4 both inclusive or a halogenated group    thereof, an arylene group or a halogenated group thereof, or a    derivative thereof.)

-   (R2 is an alkylene group with carbon number from 2 to 4 both    inclusive or a halogenated group thereof, an alkenylene group with    carbon number from 2 to 4 both inclusive or a halogenated group    thereof, an arylene group or a halogenated group thereof, or a    derivative thereof.)

-   (R3 is an organic group with “a” valency containing carbon (C) and    at least one element of oxygen (O), nitrogen (N), sulfur (S),    silicon (Si), phosphorus (P), boron (B), and halogen. “a” is one of    integer numbers from 1 to 3 both inclusive.)

-   (R4 is an alkyl group with carbon number from 2 to 10 both    inclusive, an alkenyl group with carbon number from 2 to 10 both    inclusive, a cycloalkyl group, a cycloalkenyl group, an aromatic    ring group, a heterocyclic group, or a derivative thereof.)

According to the electrolyte of the embodiment of the invention, thesolvent contains at least one of the sulfone compounds expressed byFormula (1) and Formula (2) and at least one of succinonitrile,1,6-dicyanohexane, 1,2,3-propane tricarbonitrile,7,7,8,8-tetracyanoquinodimethane, and the compounds expressed by Formula(3) to Formula (4). Thus, compared to a case that the solvent does notcontain both the sulfone compound and the compound such assuccinonitrile or a case that that the solvent contains at least onethereof, chemical stability of the electrolyte is improved. Thus,according to the secondary battery using the electrolyte, even if chargeand discharge are repeated, electrolyte decomposition reaction isinhibited. Accordingly, cycle characteristics are able to be improved.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription and the Figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross sectional view illustrating a structure of a firstsecondary battery including an electrolyte according to an embodiment ofthe present invention.

FIG. 2 is a cross sectional view illustrating an enlarged part of aspirally wound electrode body illustrated in FIG. 1.

FIG. 3 is a cross sectional view schematically illustrating a structureof the anode illustrated in FIG. 2.

FIG. 4 is a cross sectional view schematically illustrating anotherstructure of the anode illustrated in FIG. 2.

FIG. 5 illustrates an SEM photograph illustrating a cross sectionalstructure of the anode illustrated in FIG. 2 and a schematic viewthereof.

FIG. 6 illustrates an SEM photograph illustrating another crosssectional structure of the anode illustrated in FIG. 2 and a schematicview thereof.

FIG. 7 is a perspective view illustrating a structure of a thirdsecondary battery including the electrolyte according to the embodimentof the present invention.

FIG. 8 is a cross sectional view taken along line VIII-VIII of aspirally wound electrode body illustrated in FIG. 7.

FIG. 9 is a diagram illustrating an analytical result of anSnCoC-containing material by XPS.

DETAILED DESCRIPTION

A description will be hereinafter given in detail of an embodiment ofthe present invention with reference to the drawings. In addition, thedescription will be given in the following order.

-   1. Electrolyte-   2. Electrochemical device using electrolyte (secondary battery)

2-1. First secondary battery (lithium ion secondary battery: cylindricaltype)

2-2. Second secondary battery (lithium metal secondary battery:cylindrical type)

2-3. Third secondary battery (lithium ion secondary battery: laminatedfilm type)

<1. Electrolyte>

An electrolyte according to the embodiment of the present invention isused for, for example, an electrochemical device such as a secondarybattery. In the electrolyte, an electrolyte salt is dissolved in asolvent. However, the electrolyte may contain other material such asvarious additives in addition to the solvent and the electrolyte salt.

[Solvent]

The solvent contains at least one of sulfone compounds expressed byFormula (1) and Formula (2) and at least one of succinonitrile(NC—CH₂—CH₂—CN), 1,6-dicyanohexane (NC—CH₂—(CH₂)₄—CH₂—CN), 1,2,3-propanetricarbonitrile (NC—CH₂—CH(CN)—CH₂—CN), 7,7,8,8-tetracyanoquinodimethane((NC)₂C═C₆H₄═C(CN)₂), and compounds expressed by Formula (3) to Formula(5). Thereby, chemical stability of the electrolyte is improved morethan in a case that both the sulfone compound and succinonitrile or thelike are not contained or a case that only one thereof is contained. Thesulfone compounds expressed by Formula (1) and Formula (2) will behereinafter collectively referred to as “sulfone compound” according toneeds. Similarly, succinonitrile, 1,6-dicyanohexane, 1,2,3-propanetricarbonitrile, and 7,7,8,8-tetracyanoquinodimethane will becollectively referred to as “nitrile compound,” and the compoundsexpressed by Formula (3) will be collectively referred to as “isocyanatecompound.” Further, the compounds expressed by Formula (4) will becollectively referred to as “pyrrolidone compound,” and the compoundsexpressed by Formula (5) will be collectively referred to as “ethercompound.”

-   (R1 is an alkylene group with carbon number from 2 to 4 both    inclusive or a halogenated group thereof, an alkenylene group with    carbon number from 2 to 4 both inclusive or a halogenated group    thereof, an arylene group or a halogenated group thereof, or a    derivative thereof.)

-   (R2 is an alkylene group with carbon number from 2 to 4 both    inclusive or a halogenated group thereof, an alkenylene group with    carbon number from 2 to 4 both inclusive or a halogenated group    thereof, an arylene group or a halogenated group thereof, or a    derivative thereof.)

[Chemical formula 8]

R3NCO]_(a)   (3)

-   (R3 is an organic group with “a” valency containing carbon and at    least one element selected from the group consisting of oxygen,    nitrogen, sulfur, silicon, phosphorus, boron, and halogen. “a” is    one of integer numbers from 1 to 3 both inclusive.)

-   (R4 is an alkyl group with carbon number from 2 to 10 both    inclusive, an alkenyl group with carbon number from 2 to 10 both    inclusive, a cycloalkyl group, a cycloalkenyl group, an aromatic    ring group, a heterocyclic group, or a derivative thereof.)

[Chemical formula 10]

R5-O—R6   (5)

-   (R5 and R6 are an alkyl group with carbon number from 1 to 10 both    inclusive or a halogenated alkyl group with carbon number from 1 to    10 both inclusive. At least one thereof is the halogenated alkyl    group with carbon number from 1 to 10 both inclusive.)

The sulfone compound shown in Formula (1) is a cyclic compound having adisulfonic acid anhydride (—S(═O)₂—O—S(═O)₂—). Regarding R1, thealkylene group and the alkenylene group may be a straight chain orbranched group. As “halogenated group,” specially, a perfluoro group ispreferable. Further, though halogen type is not particularly limited,fluorine is specially preferable, since thereby chemical stability ofthe sulfone compound is improved. “Halogenated group” means a groupobtained by substituting some of hydrogen included in a substituentgroup such as an alkyl group by halogen. “Halogenated” used for theafter-mentioned halogenated alkyl group or the like means the samething. Further, “derivative” means a group obtained by introducing oneor two or more substituent groups to an alkyl group or the like. Thesubstituent group to be introduced may be a hydrocarbon group or a groupother than the hydrocarbon group.

Regarding RE the carbon number of the alkylene group and the alkenylenegroup is from 2 to 4 both inclusive for the following reason. That is,superior solubility and superior compatibility are thereby obtained, andchemical stability of the sulfone compound is improved. Morespecifically, in the case where the carbon number is 1, sufficientchemical stability is not able to be obtained. Meanwhile, in the casewhere the carbon number is 5 or more, sufficient solubility andsufficient compatibility are not able to be obtained.

Examples of the sulfone compound shown in Formula (1) include compoundsexpressed by Formula (1-1) to Formula (1-22). Such compounds include ageometric isomer. Specially, the compound shown in Formula (1-1) or thecompound shown in Formula (1-2) is preferable, since thereby high effectis obtained and such a compound is easily available. It is to be notedthat the sulfone compound shown in Formula (1) is not limited to thecompounds shown in Formula (1-1) to Formula (1-22), and may be othercompound.

The sulfone compound shown in Formula (2) is a cyclic compound having asulfonic acid carboxylic acid anhydride (—S(═O)₂—O—C(═O)—). Details ofthe structure and the carbon number of R2 are similar to those describedfor R1.

Examples of the sulfone compound shown in Formula (2) include compoundsexpressed by Formula (2-1) to Formula (2-20). Such compounds include ageometric isomer. Specially, the compound shown in Formula (2-1) or thecompound shown in Formula (2-2) is preferable, since thereby high effectis obtained and such a compound is easily available. It is to be notedthat the sulfone compound shown in Formula (2) is not limited to thecompounds shown in Formula (2-1) to Formula (2-20), and may be othercompound.

The nitrile compound is the foregoing succinonitrile or the like for thefollowing reason. That is, in the case where the foregoingsuccinonitrile or the like is used together with the sulfone compound,chemical stability of the electrolyte is more improved than in the casethat other compound having a cyano group (—CN) is used.

The isocyanate compound shown in Formula (3) is a compound having one,two, or three isocyanate groups (—N═C═O). The number of isocyanategroups is one, two, or three for the following reason. That is, superiorsolubility and superior compatibility are thereby obtained, and chemicalstability of the isocyanate compound is improved. That is, in the casewhere the number of isocyanate groups is four or more, sufficientsolubility, sufficient compatibility, and sufficient chemical stabilityare less likely to be obtained.

Regarding R3, the structure, the carbon number and the like arearbitrary as long as R3 is an monovalent/bivalent/trivalent organicgroup (organic group with “a” valency) containing hydrogen, oxygen orthe like described above together with carbon. Regarding R3, examples ofthe monovalent organic group include a straight chain or branched alkylgroup, a cycloalkyl group, an aromatic hydrocarbon group, a group havingether bond (—O—), and a halogenated group thereof. In the case where R3is the straight chain alkyl group, examples thereof include thefollowing group or the like. That is, a methyl group (—CH₃), an ethylgroup expressed by Formula (3-1), an n-propyl group expressed by Formula(3-2), an n-butyl group expressed by Formula (3-3), an n-pentyl groupexpressed by Formula (3-4), an n-hexyl group expressed by Formula (3-5),an n-heptyl group expressed by Formula (3-6), and an n-octyl groupexpressed by Formula (3-7). In the case where R3 is the branched alkylgroup, examples thereof include a branched alkyl group with carbonnumber from 3 to 12 both inclusive expressed by Formula (3-8) to Formula(3-28). In the case where R3 is the cycloalkyl group, examples thereofinclude a cyclohexyl group. In the case where R3 is the monovalentaromatic hydrocarbon group, examples thereof include a phenyl group(—C₆H₅) expressed by Formula (3-29) and a group obtained by binding analkylene group and an aryl group expressed by Formula (3-30) to Formula(3-35). In the case where R3 is the monovalent group having ether bond,examples thereof include a group obtained by binding an alkylene groupand an alkyl group with ether bond in between expressed by Formula(3-36) to Formula (3-63).

In the case where R3 is the halogenated group of the monovalent organicgroup, examples thereof include the following groups. That is, afluoromethyl group, a difluoromethyl group, a trifluoromethyl group, achain fluorinated alkyl group expressed by Formula (3-64) to Formula(3-79), a branched fluorinated alkyl group expressed by Formula (3-80)to Formula (3-85), and a fluorinated aromatic ring group expressed byFormula (3-86) to Formula (3-92). In this case, though halogen type isarbitrary, halogen is preferably fluorine in order to further improvechemical stability. It is to be noted that in the case where R3 is themonovalent organic group, the monovalent organic group is not limited tothe foregoing group, and may be other monovalent organic group. Examplesof other monovalent organic group include the following groups. That is,an alkenyl group such as a vinyl group, a 2-methylvinyl group, a2,2-dimethylvinyl group, a butene-2,4-diyl group, and an aryl group, analkynyl group such as an ethynyl group, a monovalent heterocyclic group,a halogenated group thereof, and a derivative thereof.

-   (x10 to x17 are one of integer numbers from 0 to 2 both inclusive.    x10 to x17 may be identical or different from each other. However,    x10+x11≧1, x12+x13≧1, x14+x15≧1, and x16+x17≧1 are satisfied.)

-   (x18 to x20, x22, x24, x26, and x28 are one of integer numbers from    0 to 3 both inclusive. x21 is one of integer numbers from 0 to 5    both inclusive. x23 is one of integer numbers from 0 to 7 both    inclusive. x25 is one of integer numbers from 0 to 9 both inclusive.    x27 is one of integer numbers from 0 to 11 both inclusive. x29 is    one of integer numbers from 0 to 13 both inclusive. x18 to x29 may    be identical or different from each other. x18+x19≧1, x20+x21≧1,    x22+x23≧1, x24+x25≧1, x26+x27≧1, and x28+x29≧1 are satisfied.)

-   (x30 is one of integer numbers from 1 to 5 both inclusive. x31, x33,    x35, x37, x39, and x41 are one of integer numbers from 0 to 5 both    inclusive. x32 is one of integer numbers from 0 to 3 both inclusive.    x34 is one of integer numbers from 0 to 5 both inclusive. x36 is one    of integer numbers from 0 to 7 both inclusive. x38 is one of integer    numbers from 0 to 9 both inclusive. x40 is one of integer numbers    from 0 to 11 both inclusive. x42 is one of integer numbers from 0 to    13 both inclusive. x30 to x42 may be identical or different from    each other. x31+x32≧1, x33+x34≧1, x35+x36≧1, x37+x38≧1, x39+x40≧1,    and x41+x42≧1 are satisfied.)

Regarding R3, examples of the divalent organic group include a straightchain or branched alkylene group, a cycloalkylene group, an aromatichydrocarbon group, a group having ether bond (—O—), and a halogenatedgroup thereof. In the case where R3 is the straight chain alkylenegroup, examples thereof include a methylene group (—CH₂—) and analkylene group with carbon number from 1 to 8 both inclusive expressedby Formula (3-93) to Formula (3-99). In the case where R3 is thebranched alkylene group, examples thereof include an alkylene group withcarbon number from 3 to 8 both inclusive expressed by Formula (3-100) toFormula (3-108). In the case where R3 is the cycloalkylene group,examples thereof include a cyclohexylene group. Further, in the casewhere R3 is the divalent aromatic hydrocarbon group, examples thereofinclude an arylene group expressed by Formula (3-109) to Formula (3-111)and a group obtained by binding two alkylene groups with an arylenegroup in between expressed by Formula (3-112) to Formula (3-114). In thecase where R3 is the divalent group having ether bond, examples thereofinclude a divalent group including ether bond and an alkylene groupexpressed by Formula (3-115) to Formula (3-127). In the case where R3 isthe halogenated group, examples thereof include a group including etherbond and a fluorinated alkylene group expressed by Formula (3-128) toFormula (3-136). It is to be noted that regarding R3, the divalentorganic group is not limited to the foregoing group, and may be otherdivalent organic group. Examples of other divalent organic group includea carbonyl group (—C(═O)—) and a group obtained by binding a carbonylgroup and an alkylene group.

Examples of the isocyanate compound shown in Formula (3) include amonoisocyanate compound, a diisocyanate compound, and a triisocyanatecompound. Examples of the monoisocyanate compound include the followingcompounds. That is, 1-isocyanatoethane (C₂H₅—NCO),3-isocyanato-1-propene (CH₂═CH—CH₂—NCO), 2-isocyanatopropane((H₃C)₂CH—NCO), 1-isocyanatopropane (H₃C—CH₂—CH₂—NCO),1-isocyanatobutane (H₃C—CH₂—CH₂—CH₂—NCO), 2-isocyanato-2-methylpropane((H₃C)₃C—NCO), 2-isocyanatobutane (H₃C—CH(NCO)—CH₂—CH₃),methylisocyanatoformate (OCN—CH₂—O—C(═O)—H), 1-isocyanatopentane(H₃C—CH₂—CH₂—CH₂—CH₂—NCO), ethylisocyanatoformate(OCN—CH₂—CH₂—O—C(═O)—H), isocyanatobenzene (C₆H₅—NCO),1-chloro-3-isocyanatopropane (OCN—CH₂—CH₂—CH₂CO₃ isocyanatocyclohexane(C₆H₁₁—NCO), isocyanatohexane (C₆H₁₃—NCO), and 1-isocyanatoheptane(C₇H₁₅—NCO). Further, examples of the diisocyanate compound include thefollowing compounds. That is, diisocyanatomethane (OCN—CH₂—NCO),1,3-diisocyanatopropane (OCN—CH₂—CH₂—CH₂—NCO), 1,4-diisocyanatobutane(OCN—CH₂—(CH₂)₂—CH₂—NCO), 1,6-diisocyanato hexane(OCN—CH₂—(CH₂)₄—CH₂—NCO), 1,8-diisocyanatooctane(OCN—CH₂—(CH₂)₆—CH₂—NCO), 1,12-diisocyanatododecane((OCN—CH₂—(CH₂)₁₀—CH₂—NCO), carbonyldiisocyanato (OCN—C(═O)—NCO),1,4-diisocyanatobutane-1,4-dione (OCN—C(═O)—(CH₂)₂—C(═O)—NCO), and1,5-diisocyanatopentane-1,5-dione (OCN—C(═O)—(CH₂)₃—C(═O)—NCO).Specially, as the isocyanate compound, 1-isocyanatopentane,1,8-dicyanatooctane, or 1,4-diisocyanatobutane-1,4-dione is preferable,since thereby higher effect is able to be obtained. It is to be notedthat the isocyanate compound is not limited to the foregoing compound,and may be other compound.

The pyrrolidone compound expressed by Formula (4) is a compound having a2-pyrrolidone skeleton. Regarding R4, the carbon number of the alkylgroup and the alkenylene group is from 2 to 10 both inclusive for thefollowing reason. That is, favorable solubility and favorablecompatibility are thereby obtained, and chemical stability is improved.More specifically, in the case where the carbon number is 1, sufficientchemical stability is not able to be obtained. Meanwhile, in the casewhere the carbon number is 11 or more, sufficient solubility andsufficient compatibility are not able to be obtained. Regarding R4,examples of the alkyl group include a straight chain or branched alkylgroup. Specific examples thereof include the alkyl group shown in theforegoing Formula (3-1) to Formula (3-24). Regarding R4, examples of thealkenyl group include a vinyl group, a 2-methylvinyl group, a2,2-dimethylvinyl group, a butene-2,4-diyl group, and an aryl group.Regarding R4, examples of the cycloalkyl group include a cyclohexylgroup, examples of the cycloalkenyl group include a cyclohexene group,and examples of the aromatic ring group include a phenyl group. Further,regarding R4, the derivative may be, for example, a halogenated group ofthe foregoing alkyl group or the like. Specifically, the derivative maybe the groups shown in the foregoing Formula (3-64) to Formula (3-92).It is to be noted that R4 is not limited to the foregoing group, and maybe a derivative other than the halogenated group thereof.

As the pyrrolidone compound shown in Formula (4), N-ethyl-2-pyrrolidone,N-propyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, orN-phenyl-2-pyrrolidone is preferable, since thereby higher effect isable to be obtained. The pyrrolidone compound is not limited to theforegoing compound, and may be other compound.

The ether compound shown in Formula (5) is a compound containing ahalogenated alkyl group and ether bond. R5 and R6 may be identical typewith each other or different type from each other. The carbon numbers ofR5 and R6 are respectively from 1 to 10 both inclusive for the followingreason. That is, favorable solubility and favorable compatibility arethereby obtained, and chemical stability is improved. Regarding R5 andR6, examples of the alkyl group include a straight chain or branchedalkyl group. Specific examples thereof include the alkyl group shown inthe foregoing Formula (3-1) to Formula (3-24) in addition to the methylgroup. Further, examples of the halogenated alkyl group include afluoromethyl group, a difluoromethyl group, a trifluoromethyl group, andthe branched fluorinated alkyl group expressed by Formula (3-64) toFormula (3-85) described above. In this case, though halogen type isarbitrary, in particular, fluorine is preferable in order to obtainhigher chemical stability.

Examples of the ether compound shown in Formula (5) include C₄F₉OCH₃,C₄F₉O ₂H₅, C₆F₁₃OCH₃, and C₃HF₆—CH(CH₃)—OC₃HF₆. Specially, C₄F₉OCH₃ orC₆F₁₃OCH₃ is preferable, since thereby higher effect is able to beobtained. It is to be noted that the ether compound is not limited tothe foregoing compound, and may be other compound.

Though the content of the sulfone compound in the electrolyte is notparticularly limited, the content is preferably 0.01 wt % or more and 5wt % or less. Further, a content of at least one of the nitrilecompound, the isocyanate compound, the pyrrolidone compound, and theether compound in the electrolyte is not particularly limited.Specially, a content of at least one of the nitrile compound, theisocyanate compound, the pyrrolidone compound, and the ether compound inthe electrolyte is preferably 0.01 wt % or more and 20 wt % or less. Inparticular, in the case where the nitrile compound or the like otherthan the ether compound is used, the content of the nitrile compound,the isocyanate compound, or the pyrrolidone compound in the electrolyteis preferably 0.01 wt % or more and 5 wt % or less. In the case wherethe ether compound is used, the content of the ether compound in theelectrolyte is preferably 5 wt % or more and 15 wt % or less. In thecase where both the sulfone compound and the nitrile compound or thelike are used in the foregoing range, chemical stability is particularlyimproved.

In addition, the solvent may contain other material as long as thesolvent contains the foregoing sulfone compound and the foregoingnitrile compound or the like. Such other material is, for example, oneor more of the nonaqueous solvents such as an organic solvent describedbelow. It is to be noted that in the after-mentioned nonaqueoussolvents, solvents corresponding to the sulfone compound and the nitrilecompound or the like are excluded.

Examples of nonaqueous solvents include the following. That is, examplesthereof include ethylene carbonate, propylene carbonate, butylenecarbonate, dimethyl carbonate, diethyl carbonate, ethyl methylcarbonate, methylpropyl carbonate, γ-butyrolactone, γ-valerolactone,1,2-dimethoxyethane, and tetrahydrofuran. Further examples thereofinclude 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane,4-methyl-1,3-dioxolane, 1,3-dioxane, and 1,4-dioxane. Furthermore,examples thereof include methyl acetate, ethyl acetate, methylpropionate, ethyl propionate, methyl butyrate, methyl isobutyrate,trimethyl methyl acetate, and trimethyl ethyl acetate. Furthermore,examples thereof include acetonitrile, glutaronitrile, adiponitrile,methoxyacetonitrile, 3-methoxypropionitrile, N,N-dimethylformamide,N-methylpyrrolidinone, and N-methyloxazolidinone. Furthermore, examplesthereof include N,N′-dimethylimidazolidinone, nitromethane, nitroethane,sulfolane, trimethyl phosphate, and dimethyl sulfoxide. Superiorcharacteristics are thereby obtained in an electrochemical device usingthe electrolyte. Such characteristics mean, for example, a batterycapacity, cycle characteristics, storage characteristics and the like inthe case where the electrolyte is used for a secondary battery.

Specially, at least one kind of ethylene carbonate, propylene carbonate,dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate ispreferable, since thereby superior battery capacity, superior cyclecharacteristics, superior storage characteristics and the like areobtained. In this case, a combination of a high viscosity (highdielectric constant) solvent (for example, specific inductive ε≧30) suchas ethylene carbonate and propylene carbonate and a low viscositysolvent (for example, viscosity≦1 mPa·s) such as dimethyl carbonate,ethylmethyl carbonate, and diethyl carbonate is more preferable.Thereby, dissociation property of the electrolyte salt and ion mobilityare improved.

In particular, the solvent preferably contains at least one of ahalogenated chain ester carbonate expressed by Formula (6) and ahalogenated cyclic ester carbonate expressed by Formula (7). Thereby, inthe case where the solvent is used for an electrochemical device, astable protective film is formed on the surface of the electrode at thetime of electrode reaction, and thus decomposition reaction of theelectrolyte is inhibited. “Halogenated chain ester carbonate” is a chainester carbonate containing halogen as an element. “Halogenated cyclicester carbonate” is a cyclic ester carbonate containing halogen as anelement. R11 to R16 in Formula (6) may be identical type with each otheror different type from each other. The same is applied to R17 to R20 inFormula (7). The content of the halogenated chain ester carbonate andthe content of the halogenated cyclic ester carbonate in the solventare, for example, from 0.01 wt % to 50 wt % both inclusive. However, thetype of the halogenated chain ester carbonate or the halogenated cyclicester carbonate is not necessarily limited to the compounds describedbelow, and may be other compound.

-   (R11 to R16 are a hydrogen group, a halogen group, an alkyl group,    or a halogenated alkyl group. At least one of R11 to R16 is the    halogen group or the halogenated alkyl group.)

-   (R17 to R20 are a hydrogen group, a halogen group, an alkyl group,    or a halogenated alkyl group. At least one of R17 to R20 is the    halogen group or the halogenated alkyl group.)

The halogen type is not particularly limited, but specially, fluorine,chlorine, or bromine is preferable, and fluorine is more preferablesince thereby higher effect is obtained compared to other halogen. Thenumber of halogen is more preferably two than one, and further may bethree or more for the following reason. That is, in the case where theelectrolyte is used for an electrochemical device such as a secondarybattery, at the time of electrode reaction, an ability to form aprotective film on the electrode surface is improved, and a more rigidand stable protective film is formed. Accordingly, decompositionreaction of the electrolyte is more inhibited.

Examples of the halogenated chain ester carbonate include fluoromethylmethyl carbonate, bis(fluoromethyl) carbonate, and difluoromethyl methylcarbonate. Examples of the halogenated cyclic ester carbonates includecompounds expressed by Formula (7-1) to Formula (7-21). That is,examples thereof include 4-fluoro-1,3-dioxolane-2-one of Formula (7-1),4-chloro-1,3-dioxolane-2-one of Formula (7-2),4,5-difluoro-1,3-dioxolane-2-one of Formula (7-3),tetrafluoro-1,3-dioxolane-2-one of Formula (7-4),4-chloro-5-fluoro-1,3-dioxolane-2-one of Formula (7-5),4,5-dichloro-1,3-dioxolane-2-one of Formula (7-6),tetrachloro-1,3-dioxolane 2-one of Formula (7-7), 4,5-bis trifluoromethyl-1,3-dioxolane 2-one of Formula (7-8), 4-trifluoromethyl-1,3-dioxolane-2-one of Formula (7-9),4,5-difluoro-4,5-dimethyl-1,3-dioxolane-2-one of Formula (7-10),4,4-difluoro-5-methyl-1,3-dioxolane-2-one of Formula (7-11),4-ethyl-5,5-difluoro-1,3-dioxolane-2-one of Formula (7-12),4-fluoro-5-trifluoromethyl-1,3-dioxolane-2-one of Formula (7-13),4-methyl-5-trifluoro-methyl-1,3-dioxolane-2-one of Formula (7-14),4-fluoro-4,5-dimethyl-1,3-dioxolane-2-one of Formula (7-15),5-(1,1-difluoroethyl)-4,4-difluoro1,3-dioxolane-2-one of Formula (7-16),4,5-dichloro-4,5-dimethyl-1,3-dioxolane-2-one of Formula (7-17),4-ethyl-5-fluoro-1,3-dioxolane-2-one of Formula (7-18),4-ethyl-4,5-difluoro-1,3-dioxolane-2-one of Formula (7-19),4-ethyl-4,5,5-trifluoro-1,3-dioxolane-2-one of Formula (7-20), and4-fluoro-4-methyl-1,3-dioxolane-2-one of Formula (7-21). The geometricisomer is included in the halogenated cyclic ester carbonate. Specially,4-fluoro-1,3-dioxolane-2-one shown in Formula (7-1) or4,5-difluoro-1,3-dioxolane-2-one shown in Formula (7-3) is preferable,and 4,5-difluoro-1,3-dioxolane-2-one is more preferable. In particular,as 4,5-difluoro-1,3-dioxolane-2-one, a trans isomer is more preferablethan a cis isomer, since the trans isomer is easily available andprovides high effect.

Further, the solvent preferably contains at least one of unsaturatedcarbon bond cyclic ester carbonates expressed by Formula (8) to Formula(10) for the following reason. That is, in the case where the solvent isused for an electrochemical device, at the time of electrode reaction, astable protective film is formed on the electrode surface, andaccordingly decomposition reaction of the electrolyte is inhibited.“Unsaturated carbon bond cyclic ester carbonate” is a cyclic estercarbonate having unsaturated carbon bond. The content of the unsaturatedcarbon bond cyclic ester carbonate in the solvent is, for example, from0.01 wt % to 10 wt % both inclusive. The type of the unsaturated carbonbond cyclic ester carbonate is not limited to types described below, andmay be other type.

-   (R21 and R22 are a hydrogen group or an alkyl group.)

-   (R23 to R26 are a hydrogen group, an alkyl group, a vinyl group, or    an aryl group. At least one of R23 to R26 is the vinyl group or the    aryl group.)

-   (R27 is an alkylene group.)

The unsaturated carbon bond cyclic ester carbonate shown in Formula (8)is a vinylene carbonate compound. Examples of the vinylene carbonatecompound include the following compounds. That is, vinylene carbonate,methylvinylene carbonate, ethylvinylene carbonate,4,5-dimethyl-1,3-dioxole-2-one, 4,5-diethyl-1,3-dioxole-2-one,4-fluoro-1,3-dioxole-2-one, and 4-trifluoromethyl-1,3-dioxole-2-one.Specially, vinylene carbonate is preferable, since vinylene carbonate iseasily available and provides high effect.

The unsaturated carbon bond cyclic ester carbonate shown in Formula (9)is a vinylethylene carbonate compound. Examples of the vinylethylenecarbonate compound include the following compounds. That is,vinylethylene carbonate, 4-methyl-4-vinyl-1,3-dioxolane-2-one,4-ethyl-4-vinyl-1,3-dioxolane-2-one,4-n-propyl-4-vinyl-1,3-dioxolane-2-one,5-methyl-4-vinyl-1,3-dioxolane-2-one, 4,4-divinyl-1,3-dioxolane-2-one,and 4,5-divinyl-1,3-dioxolane-2-one. Specially, vinylethylene carbonateis preferable, since vinylethylene carbonate is easily available, andprovides high effect. It is needless to say that all of R23 to R26 maybe the vinyl group or the aryl group. Otherwise, it is possible thatsome of R23 to R26 are the vinyl group, and the others thereof are thearyl group.

The unsaturated carbon bond cyclic ester carbonate shown in Formula (10)is a methylene ethylene carbonate compound. Examples of the methyleneethylene carbonate compound include 4-methylene-1,3-dioxolane-2-one,4,4-dimethyl-5-methylene-1,3-dioxolane-2-one, and4,4-diethyl-5-methylene-1, 3-dioxolane-2-one. The methylene ethylenecarbonate compound may have one methylene group (compound shown inFormula (10)), or may have two methylene groups.

In addition, the unsaturated carbon bond cyclic ester carbonate may becatechol carbonate having a benzene ring or the like, in addition to thecompounds shown in Formula (8) to Formula (10).

Moreover, the solvent preferably contains sultone (cyclic sulfonicester), since thereby chemical stability of the electrolyte is moreimproved. Examples of sultone include propane sultone and propenesultone. The sultone content in the solvent is, for example, from 0.5 wt% to 5 wt % both inclusive. The sultone type is not necessarily limitedto the foregoing type, and may be other type.

Further, the solvent preferably contains an acid anhydride, sincethereby chemical stability of the electrolyte is more improved. Examplesof the acid anhydride include carboxylic anhydride such as succinicanhydride, glutaric anhydride, and maleic anhydride. The content of theacid anhydride in the solvent is, for example, from 0.5 wt % to 5 wt %both inclusive. However, the acid anhydride type is not necessarilylimited to the foregoing type, and maybe other type.

The inherent viscosity of the solvent is, for example, preferably 10.0mPa·s or less at 25 deg C., since thereby dissociation property of theelectrolyte salt and ion mobility are able to be secured. In addition,the inherent viscosity in a state that the electrolyte salt is dissolvedin the solvent (that is, inherent viscosity of the electrolyticsolution) is also preferably 10.0 mPa·s or less at 25 deg C. for asimilar reason.

[Electrolyte Salt]

The electrolyte salt contains, for example, any one or more of lightmetal salts such as a lithium salt. However, the electrolyte salt maycontain, for example, a salt other than a light metal salt.

Examples of lithium salts include the following. That is, examplesthereof include lithium hexafluorophosphate, lithium tetrafluoroborate,lithium perchlorate, and lithium hexafluoroarsenate. Further, examplesthereof include lithium tetraphenylborate (LiB(C₆H₅)₄), lithiummethanesulfonate (LiCH₃SO₃), lithium trifluoromethane sulfonate(LiCF₃SO₃), and lithium tetrachloroaluminate (LiAlCl₄). Further,examples thereof include dilithium hexafluorosilicate (Li₂SiF₆), lithiumchloride (LiCl), lithium bromide (LiBr), lithium monofluorophosphate(LiPFO₃), and lithium difluorophosphate (LiPF₂O₂). Thereby, superiorcharacteristics are obtained in an electrochemical device using theelectrolyte. The type of electrolyte salt is not necessarily limited tothe foregoing type, but may be other type.

Specially, at least one of lithium hexafluorophosphate, lithiumtetrafluoroborate, lithium perchlorate, and lithium hexafluoroarsenateis preferable, and lithium hexafluorophosphate is more preferable, sincethe internal resistance is lowered, and thus higher effect is obtained.In particular, both lithium hexafluorophosphate and lithiumtetrafluoroborate are preferably used, since thereby high effect is ableto be obtained.

In particular, the electrolyte salt preferably contains at least onekind of the compounds expressed by Formula (11) to Formula (13), sincethereby higher effect is able to be obtained. It is to be noted that R33in Formula (11) may be identical or different. The same is applied toR41 to R43 in Formula (12) and R51 and R52 in Formula (13).

-   (X31 is a Group 1 element or a Group 2 element in the long period    periodic table or aluminum. M31 is a transition metal element, a    Group 13 element, a Group 14 element, or a Group 15 element in the    long period periodic table. R31 is a halogen group. Y31 is    —OC—R32-CO—, —OC—C(R33)₂—, or —OC—CO—. However, R32 is an alkylene    group, a halogenated alkylene group, an arylene group, or a    halogenated arylene group. R33 is an alkyl group, a halogenated    alkyl group, an aryl group, or a halogenated aryl group. In    addition, a3 is one of integer numbers 1 to 4. b3 is 0, 2, or 4. c3,    d3, m3, and n3 are one of integer numbers 1 to 3.)

-   (X41 is a Group 1 element or a Group 2 element in the long period    periodic table. M41 is a transition metal element, a Group 13    element, a Group 14 element, or a Group 15 element in the long    period periodic table. Y41 is —OC—(C(R41)₂)_(b4)-CO—,    —(R43)₂C—(C(R42)₂)_(c4)-CO—, —(R43)₂C—(C(R42)₂)_(c4)-C(R43)₂—,    —(R43)₂C—(C(R42)₂)_(c4)-SO₂—, —O₂S—(C(R42)₂)_(d4)-SO₂—, or    —OC—(C(R42)₂)_(d4)-SO₂—. However, R41 and R43 are a hydrogen group,    an alkyl group, a halogen group, or a halogenated alkyl group. At    least one of R41/R43 is respectively the halogen group or the    halogenated alkyl group. R42 is a hydrogen group, an alkyl group, a    halogen group, or a halogenated alkyl group. In addition, a4, e4,    and n4 are 1 or 2. b4 and d4 are one of integer numbers 1 to 4. c4    is one of integer numbers 0 to 4. f4 and m4 are one of integer    numbers 1 to 3.)

-   (X51 is a Group 1 element or a Group 2 element in the long period    periodic table. M51 is a transition metal element, a Group 13    element, a Group 14 element, or a Group 15 element in the long    period periodic table. Rf is a fluorinated alkyl group with carbon    number from 1 to 10 both inclusive or a fluorinated aryl group with    carbon number from 1 to 10 both inclusive. Y51 is    —OC—(C(R51)₂)_(d5)-CO—, —(R52)₂C—(C(R51)₂)_(d5)-CO—,    —(R52)₂C—(C(R51)₂)_(d5)-C(R52)₂—, —(R52)₂C—(C(R51)₂)_(d5)-SO₂—,    —O₂S—(C(R51)₂)_(e5)-SO₂—, or —OC—(C(R51)₂)_(e5)-SO₂—. However, R51    is a hydrogen group, an alkyl group, a halogen group, or a    halogenated alkyl group. R52 is a hydrogen group, an alkyl group, a    halogen group, or a halogenated alkyl group, and at least one    thereof is the halogen group or the halogenated alkyl group. In    addition, a5, f5, and n5 are 1 or 2. b5, c5, and e5 are one of    integer numbers 1 to 4. d5 is one of integer numbers 0 to 4. g5 and    m5 are one of integer numbers 1 to 3.)

It is to be noted that Group 1 element in the long period periodic tablerepresents hydrogen (H), lithium (Li), sodium (Na), potassium (K),rubidium (Rb), cesium (Cs), and francium (Fr). Group 2 elementrepresents beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr),barium (Ba), and radium (Ra). Group 13 element represents boron,aluminum (Al), gallium (Ga), indium (In), and thallium (Tl). Group 14element represents carbon, silicon, germanium (Ge), tin (Sn), and lead(Pb). Group 15 element represents nitrogen, phosphorus, arsenic (As),antimony (Sb), and bismuth (Bi).

Examples of the compound shown in Formula (11) include compoundsexpressed by Formula (11-1) to Formula (11-6). Examples of the compoundshown in Formula (12) include compounds expressed by Formula (12-1) toFormula (12-8). Examples of the compound shown in Formula (13) include acompound expressed by Formula (13-1).

Further, the electrolyte salt preferably contains at least one ofcompounds expressed by Formula (14) to Formula (16), since therebyhigher effect is able to be obtained. m and n in Formula (14) may be thesame value or a value different from each other. The same is applied top, q, and r in Formula (16). However, the type of the electrolyte saltis not necessarily limited to the type described below, and may be othertype.

LiN(C_(m)F_(2m+1)SO₂)(C_(n)F_(2n+1)SO₂)   (14)

(m and n are an integer number equal to or greater than 1.)

-   (R61 is a straight chain or branched perfluoro alkylene group with    carbon number from 2 to 4 both inclusive.)

LiC(C_(p)F_(2p+1)SO₂)(C_(q)F_(2q+1)SO₂)(C_(r)F_(2r+1)SO₂)   (16)

(p, q, and r are an integer number of 1 or more.)

The compound shown in Formula (14) is a chain imide compound. Examplesof the compound include the following compounds. That is, examplesthereof include lithium bis(trifluoromethanesulfonyl)imide(LiN(CF₃SO₂)₂) and lithium bis(pentafluoroethanesulfonyl)imide(LiN(C₂F₅SO₂)₂). Further examples thereof includelithium(trifluoromethanesulfonyl)(pentafluoroethanesulfonyl)imide(LiN(CF₃SO₂)(C₂F₅SO₂)). Further examples thereof includelithium(trifluoromethanesulfonyl)(heptafluoropropanesulfonyl)imide(LiN(CF₃SO₂)(C₃F₇SO₂)). Further examples thereof includelithium(trifluoromethanesulfonyl)(nonafluorobutanesulfonyl)imide(LiN(CF₃SO₂)(C₄F₉SO₂)).

The compound shown in Formula (15) is a cyclic imide compound. Examplesof the compound include compounds expressed by Formula (15-1) to Formula(15-4). That is, examples thereof include lithium1,2-perfluoroethanedisulfonyl imide of Formula (15-1) or lithium1,3-perfluoropropanedisulfonyl imide of Formula (15-2), lithium1,3-perfluorobutanedisulfonyl imide of Formula (15-3), and lithium1,4-perfluorobutanedisulfonyl imide of Formula (15-4).

The compound shown in Formula (16) is a chain methyde compound. Examplesof the compound include lithium tris(trifluoromethanesulfonyl)methyde(LiC(CF₃SO₂)₃).

The content of the electrolyte salt to the solvent is preferably from0.3 mol/kg to 3.0 mol/kg both inclusive, since thereby high ionconductivity is obtained.

In the electrolyte, the solvent contains at least one kind of thesulfone compounds and at least one of the nitrile compound, theisocyanate compound, the pyrrolidone compound, and the ether compound.

A description will be given of a case that an electrolyte containingeither the sulfone compound or the nitrile compound or the like is usedas a solvent for an electrochemical device. If only the sulfone compoundis used out of the sulfone compound and the nitrile compound or thelike, decomposition reaction of the electrolyte at the time of electrodereaction is slightly inhibited, but is not sufficiently inhibited.Meanwhile, if only the nitrile compound or the like is used,decomposition reaction of the electrolyte at the time of electrodereaction, in particular, at the time of repeated electrode reaction isimproved. That is, in the case where only the sulfone compound is addedto the electrolyte, sufficient chemical stability is not able to beobtained. Meanwhile, in the case where only the succinonitrile or thelike is added to the electrolyte, chemical stability is significantlylowered.

However, in using combination of the sulfone compound and the nitrilecompound or the like that are not able to provide sufficient chemicalstability if being used singly, due to synergetic effect thereof,electrolyte decomposition inhibition effect at the time of electrodereaction is significantly demonstrated. That is, according to theelectrolyte in this embodiment, since combination of the sulfonecompound and the nitrile compound or the like is used, chemicalstability of the electrolyte is more improved than in a case that boththereof are not contained or a case that only one thereof is contained.Thereby, the electrolyte according to this embodiment is able tocontribute to improve performance of an electrochemical device using theelectrolyte containing the sulfone compound and the nitrile compound orthe like.

In particular, in the case where the solvent contains at least one kindof the halogenated chain ester carbonate, the halogenated cyclic estercarbonate, the unsaturated carbon bond cyclic ester carbonate, sultone,and the acid anhydride, higher effect is able to be obtained. Further,in the case where the electrolyte salt contains at least one kind oflithium hexafluorophosphate, lithium tetrafluoroborate, lithiumperchlorate, lithium hexafluoroarsenate, and the compounds shown inFormula (11) to Formula (16), higher effect is able to be obtained.

<2. Electrochemical Device (Secondary Battery) Using Electrolyte>

Next, a description will be given of usage examples of the foregoingelectrolyte. In the description, a secondary battery will be taken as anexample of electrochemical devices. The foregoing electrolyte is used asfollows.

<2-1. First Secondary Battery>

FIG. 1 and FIG. 2 illustrate a cross sectional structure of a firstsecondary battery. FIG. 2 illustrates an enlarged part of a spirallywound electrode body 20 illustrated in FIG. 1. The secondary batteryherein described is, for example, a lithium ion secondary battery inwhich the anode capacity is expressed by insertion and extraction oflithium ion as an electrode reactant.

[Whole Structure of Secondary Battery]

The secondary battery mainly contains the spirally wound electrode body20 and a pair of insulating plates 12 and 13 inside a battery can 11 inthe shape of an approximately hollow cylinder. The battery structureusing such a battery can 11 is called cylindrical type.

The battery can 11 has a hollow structure in which one end of thebattery can 11 is closed and the other end of the battery can 11 isopened. The battery can 11 is made of iron (Fe), aluminum (Al), an alloythereof or the like. In addition, in the case where the battery can 11is made of iron, for example, plating of nickel (Ni) or the like may beprovided on the surface of the battery can 11. The pair of insulatingplates 12 and 13 is arranged to sandwich the spirally wound electrodebody 20 in between from the upper and the lower sides, and to extendperpendicularly to the spirally wound periphery face.

At the open end of the battery can 11, a battery cover 14, a safetyvalve mechanism 15, and a PTC (Positive Temperature Coefficient) device16 are attached by being caulked with a gasket 17. Inside of the batterycan 11 is hermetically sealed. The battery cover 14 is made of, forexample, a material similar to that of the battery can 11. The safetyvalve mechanism 15 and the PTC device 16 are provided inside of thebattery cover 14. The safety valve mechanism 15 is electricallyconnected to the battery cover 14 through the PTC device 16. In thesafety valve mechanism 15, in the case where the internal pressurebecomes a certain level or more by internal short circuit, externalheating or the like, a disk plate 15A flips to cut the electricconnection between the battery cover 14 and the spirally wound electrodebody 20. As temperature rises, the PTC device 16 increases theresistance (limits a current) to prevent abnormal heat generationresulting from a large current. The gasket 17 is made of, for example,an insulating material. The surface of the gasket 17 is coated with, forexample, asphalt.

In the spirally wound electrode body 20, a cathode 21 and an anode 22are layered with a separator 23 in between and spirally wound. A centerpin 24 may be inserted in the center of the spirally wound electrodebody 20. In the spirally wound electrode body 20, a cathode lead 25 madeof aluminum or the like is connected to the cathode 21, and an anodelead 26 made of nickel or the like is connected to the anode 22. Thecathode lead 25 is electrically connected to the battery cover 14 by,for example, being welded to the safety valve mechanism 15. The anodelead 26 is, for example, welded and thereby electrically connected tothe battery can 11.

[Cathode]

In the cathode 21, for example, a cathode active material layer 21B isprovided on both faces of a cathode current collector 21A. However, thecathode active material layer 21B may be provided only on a single faceof the cathode current collector 21A.

The cathode current collector 21A is made of, for example, aluminum,nickel, stainless (SUS) or the like.

The cathode active material layer 21B contains, as a cathode activematerial, one or more kinds of cathode materials capable of insertingand extracting lithium ions. According to needs, the cathode activematerial layer 21B may contain other material such as a cathode binderand a cathode electrical conductor.

As the cathode material, a lithium-containing compound is preferable,since thereby a high energy density is able to be obtained. Examples ofthe lithium-containing compound include a composite oxide containinglithium and a transition metal element as a constituent element and aphosphate compound containing lithium and a transition metal element asa constituent element. Specially, a compound containing at least one ofcobalt (Co), nickel, manganese (Mn), and iron as a transition metalelement is preferable, since thereby a higher voltage is obtained. Thechemical formula thereof is expressed by, for example, Li_(x)MlO₂ orLi_(y)M2PO₄. In the formula, M1 and M2 represent one or more kinds oftransition metal elements. In addition, values of x and y vary accordingto the charge and discharge state, and are generally in the range of0.05≦x≦1.10 and 0.05≦y≦1.10.

Examples of the composite oxide containing lithium and a transitionmetal element include a lithium-cobalt composite oxide (Li_(x)CoO₂), alithium-nickel composite oxide (Li_(x)NiO₂), and a lithium-nickel-basedcomposite oxide expressed by Formula (17). Further, examples of thephosphate compound containing lithium and a transition metal elementinclude lithium-iron phosphate compound (LiFePO₄) and alithium-iron-manganese phosphate compound (LiFe_(1-u)Mn_(u)PO₄ (u<1)),since thereby a high battery capacity is obtained and superior cyclecharacteristics are obtained.

LiNi_(1-x)M_(x)O₂   (17)

(M is at least one kind of cobalt, manganese, iron, aluminum, vanadium(V), tin, magnesium, titanium (Ti), strontium, calcium, zirconium (Zr),molybdenum (Mo), technetium (Tc), ruthenium (Ru), tantalum (Ta),tungsten (W), rhenium (Re), ytterbium (Yb), copper (Cu), zinc (Zn),barium, boron, chromium (Cr), silicon, gallium, phosphorus, antimony,and niobium (Nb). x is in the range of 0.005≦x≦0.5.)

In addition, examples of cathode material include an oxide, a disulfide,a chalcogenide, and a conductive polymer. Examples of the oxide includetitanium oxide, vanadium oxide, and manganese dioxide. Examples of thedisulfide include titanium disulfide and molybdenum sulfide. Examples ofthe chalcogenide include niobium selenide. Examples of the conductivepolymer include sulfur, polyaniline, and polythiophene.

It is needless to say that the cathode material may be a material otherthan the foregoing compounds. Further, two or more kinds of theforegoing cathode materials may be used by mixture arbitrary.

Examples of cathode binders include a synthetic rubber such as styrenebutadiene rubber, fluorinated rubber, and ethylene propylene diene; anda polymer material such as polyvinylidene fluoride. One thereof may beused singly, or a plurality thereof may be used by mixture.

Examples of cathode electrical conductors include a carbon material suchas graphite, carbon black, acetylene black, and Ketjen black. Such acarbon material may be used singly, or a plurality thereof may be usedby mixture. In addition, the cathode electrical conductor may be a metalmaterial, a conductive polymer or the like as long as the material hasthe electric conductivity.

[Anode]

In the anode 22, for example, an anode active material layer 22B isprovided on both faces of an anode current collector 22A. However, theanode active material layer 22B may be provided only on a single face ofthe anode current collector 22A.

The anode current collector 22A is made of, for example, copper, nickel,stainless or the like. The surface of the anode current collector 22A ispreferably roughened. Thereby, due to the so-called anchor effect, thecontact characteristics between the anode current collector 22A and theanode active material layer 22B are improved. In this case, it is enoughthat at least the surface of the anode current collector 22A in theregion opposed to the anode active material layer 22B is roughened.Examples of roughening methods include a method of forming fineparticles by electrolytic treatment. The electrolytic treatment is amethod of providing concavity and convexity by forming fine particles onthe surface of the anode current collector 22A by using electrolyticmethod in an electrolytic bath. A copper foil formed by electrolyticmethod including the copper foil roughened by the foregoing electrolytictreatment is generally called “electrolytic copper foil.”

The anode active material layer 22B contains one or more kinds of anodematerials capable of inserting and extracting lithium ions as an anodeactive material, and may also contain other material such as an anodebinder and an anode electrical conductor according to needs. It is to benoted that details of the anode binder and the anode electricalconductor are, for example, respectively similar to those of the cathodebinder and the cathode electrical conductor. In the anode activematerial layer 22B, the chargeable capacity of the anode material ispreferably larger than the discharge capacity of the cathode 21 in orderto prevent unintentional precipitation of lithium metal at the time ofcharge and discharge, for example.

Examples of anode materials include a carbon material. In the carbonmaterial, crystal structure change associated with insertion andextraction of lithium ions is extremely small. Thus, the carbon materialprovides a high energy density and superior cycle characteristics, andfunctions as an anode electrical conductor as well. Examples of carbonmaterials include graphitizable carbon, non-graphitizable carbon inwhich the spacing of (002) plane is 0.37 nm or more, and graphite inwhich the spacing of (002) plane is 0.34 nm or less. More specifically,examples of carbon materials include pyrolytic carbon, coke, glassycarbon fiber, an organic polymer compound fired body, activated carbon,and carbon black. Of the foregoing, the coke includes pitch coke, needlecoke, and petroleum coke. The organic polymer compound fired body isobtained by firing and carbonizing a phenol resin, a furan resin or thelike at appropriate temperature. In addition, the shape of the carbonmaterial may be any of a fibrous shape, a spherical shape, a granularshape, and a scale-like shape.

Moreover, examples of anode materials include a material (metalmaterial) containing at least one kind of metal elements and metalloidelements as a constituent element. By using such an anode material, ahigh energy density is able to be obtained. Such a material may be asimple substance, an alloy, or a compound of a metal element or ametalloid element, may be two or more kinds thereof, or may have one ormore kinds of phases thereof at least in part. It is to be noted that inthe present invention, “alloy” includes an alloy containing one or morekinds of metal elements and one or more kinds of metalloid elements, inaddition to an alloy composed of two or more kinds of metal elements.Further, “alloy” may contain a nonmetallic element. The texture thereofincludes a solid solution, a eutectic crystal (eutectic mixture), anintermetallic compound, and a texture in which two or more thereofcoexist.

The foregoing metal element or the foregoing metalloid element is ametal element or a metalloid element capable of forming an alloy withlithium. Specifically, the foregoing metal element or the foregoingmetalloid element is at least one kind of the following elements. Thatis, the foregoing metal element or the foregoing metalloid element ismagnesium, boron, aluminum, gallium, indium, silicon, germanium, tin,lead, bismuth, cadmium (Cd), silver (Ag), zinc, hafnium (Hf), zirconium,yttrium, palladium (Pd), and platinum (Pt). Specially, at least one ofsilicon and tin is preferable. Silicon and tin have superior ability toinsert and extract lithium ion, and thus are able to provide a highenergy density.

A material containing at least one of silicon and tin may be, forexample, a simple substance, an alloy, or a compound of silicon or tin;two or more kinds thereof; or a material having one or more kinds ofphases thereof at least in part.

Examples of alloys of silicon include an alloy containing at least oneof the following elements as a constituent element other than silicon.Such an element other than silicon is tin, nickel, copper, iron, cobalt,manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony,and chromium. Examples of compounds of silicon include a compoundcontaining oxygen or carbon as a constituent element other than silicon.In addition, the compounds of silicon may contain, for example, one ormore kinds of the elements described for the alloys of silicon as anelement other than silicon.

Examples of an alloy or a compound of silicon include the followings.That is, SiB₄, SiB₆, Mg₂Si, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂,CrSi₂, Cu₅Si, FeSi₂, MnSi₂, NbSi₂, TaSi₂, VSi₂, WSi₂, ZnSi₂, SiC, Si₃N₄,Si₂N₂O, SiO_(v) (0<v≦2), and LiSiO.

Examples of alloys of tin include an alloy containing at least one kindof the following elements as an element other than tin. Such an elementis silicon, nickel, copper, iron, cobalt, manganese, zinc, indium,silver, titanium, germanium, bismuth, antimony, or chromium. Examples ofcompounds of tin include a compound containing oxygen or carbon. Inaddition, the compounds of tin may contain one or more kinds of elementsdescribed for the alloys of tin as a constituent element other than tin.Examples of alloys or compounds of tin include SnO_(w) (0<w≦2), SnSiO₃,LiSnO, and Mg₂Sn.

In particular, as a material containing silicon, for example, the simplesubstance of silicon is preferable, since a high battery capacity,superior cycle characteristics and the like are thereby obtained. It isto be noted that “simple substance” only means a general simplesubstance (may contain a slight amount of impurity), but does notnecessarily mean a substance with purity of 100%.

Further, as a material containing tin, for example, a materialcontaining a second constituent element and a third constituent elementin addition to tin as a first constituent element is preferable. Thesecond constituent element is, for example, at least one of thefollowing elements. That is, cobalt, iron, magnesium, titanium,vanadium, chromium, manganese, nickel, copper, zinc, gallium, zirconium,niobium, molybdenum, silver, indium, cerium (Ce), hafnium, tantalum,tungsten, bismuth, and silicon. The third constituent element is, forexample, at least one kind of boron, carbon, aluminum, and phosphorus.In the case where the second constituent element and the thirdconstituent element are contained, a high battery capacity, superiorcycle characteristics and the like are able to be obtained.

Specially, a material containing tin, cobalt, and carbon(SnCoC-containing material) is preferable. As the composition of theSnCoC-containing material, for example, the carbon content is from 9.9mass % to 29.7 mass t % both inclusive, and the ratio of tin and cobaltcontents (Co/(Sn+Co)) is from 20 mass % to 70 mass % both inclusive,since a high energy density is obtained in such a composition range.

The SnCoC-containing material preferably has a phase containing tin,cobalt, and carbon. Such a phase preferably has a low crystallinestructure or an amorphous structure. The phase is a reaction phasecapable of being reacted with lithium. Due to existence of the reactionphase, superior characteristics are able to be obtained. The half-widthof the diffraction peak obtained by X-ray diffraction of the phase ispreferably 1.0 deg or more based on diffraction angle of 2θ in the casewhere CuKα ray is used as a specific X ray, and the insertion rate is 1deg/min. Thereby, lithium ions are more smoothly inserted and extracted,and reactivity with the electrolyte is decreased. In addition, theSnCoC-containing material has a phase containing a simple substance orpart of the respective elements in addition to the low crystalline oramorphous phase in some cases.

Whether or not the diffraction peak obtained by X-ray diffractioncorresponds to the reaction phase capable of being reacted with lithiumis able to be easily determined by comparison between X-ray diffractioncharts before and after electrochemical reaction with lithium. Forexample, in the case where the position of the diffraction peak afterelectrochemical reaction with lithium is changed from the position ofthe diffraction peak before electrochemical reaction with lithium, theobtained diffraction peak corresponds to the reaction phase capable ofbeing reacted with lithium. In this case, for example, the diffractionpeak of the low crystalline or amorphous reaction phase is shown in therange of 2θ=from 20 to 50 deg both inclusive. Such a reaction phasecontains, for example, the foregoing respective constituent elements,and the low crystalline or amorphous structure may result from existenceof carbon.

In the SnCoC-containing material, at least part of carbon as aconstituent element is preferably bonded to a metal element or ametalloid element as other constituent element, since therebyaggregation or crystallization of tin or the like is inhibited. Thebonding state of elements is able to be checked by, for example, X-rayPhotoelectron Spectroscopy (XPS). In a commercially available apparatus,for example, as a soft X ray, Al-Kα ray, Mg-Kα ray or the like is used.In the case where at least part of carbon is bonded to a metal element,a metalloid element or the like, the peak of a synthetic wave of 1sorbit of carbon (Cis) is shown in a region lower than 284.5 eV. Inaddition, in the apparatus, energy calibration is made so that the peakof 4f orbit of gold atom (Au4f) is obtained at 84.0 eV. At this time, ingeneral, since surface contamination carbon exists on the materialsurface, the peak of Cls of the surface contamination carbon is regardedas 284.8 eV, which is used as the energy reference. In XPS measurement,the waveform of the peak of Cls is obtained as a form including the peakof the surface contamination carbon and the peak of carbon in theSnCoC-containing material. Thus, for example, analysis is made by usingcommercially available software to isolate both peaks from each other.In the waveform analysis, the position of a main peak existing on thelowest bound energy side is the energy reference (284.8 eV).

In addition, the SnCoC-containing material may further contain otherelement according to needs. Examples of other elements include at leastone kind of silicon, iron, nickel, chromium, indium, niobium, germanium,titanium, molybdenum, aluminum, phosphorus, gallium, and bismuth.

In addition to the SnCoC-containing material, a material containing tin,cobalt, iron, and carbon (SnCoFeC-containing material) is alsopreferable. The composition of the SnCoFeC-containing material is ableto be arbitrary set. For example, a composition in which the ironcontent is set small is as follows. That is, the carbon content is from9.9 mass % to 29.7 mass % both inclusive, the iron content is from 0.3mass % to 5.9 mass % both inclusive, and the ratio of contents of tinand cobalt (Co/(Sn+Co)) is from 30 mass % to 70 mass % both inclusive.Further, for example, a composition in which the iron content is setlarge is as follows. That is, the carbon content is from 11.9 mass % to29.7 mass % both inclusive, the ratio of contents of tin, cobalt, andiron ((Co+Fe)/(Sn+Co+Fe)) is from 26.4 mass % to 48.5 mass % bothinclusive, and the ratio of contents of cobalt and iron (Co/(Co+Fe)) isfrom 9.9 mass % to 79.5 mass % both inclusive. In such a compositionrange, a high energy density is able to be obtained. The physicalproperty (half-width or the like) of the SnCoFeC-containing material issimilar to that of the foregoing SnCoC-containing material.

Further, examples of other anode materials include a metal oxide and apolymer compound. The metal oxide is, for example, iron oxide, rutheniumoxide, molybdenum oxide or the like. The polymer compound is, forexample, polyacetylene, polyaniline, polypyrrole or the like.

It is needless to say that the anode material may be a material otherthan the foregoing materials. Further, two or more of the foregoinganode active materials may be used by mixture arbitrary.

The anode active material layer 22B is formed by, for example, coatingmethod, vapor-phase deposition method, liquid-phase deposition method,spraying method, firing method (sintering method), or a combination oftwo or more kinds of these methods. Coating method is a method in which,for example, after a particulate anode active material is mixed with ananode binder or the like, the mixture is dispersed in a solvent, and theanode current collector is coated with the resultant. Examples ofvapor-phase deposition methods include physical deposition method andchemical deposition method. Specifically, examples thereof includevacuum evaporation method, sputtering method, ion plating method, laserablation method, thermal CVD (Chemical Vapor Deposition) method, andplasma CVD method. Examples of liquid-phase deposition methods includeelectrolytic plating method and electroless plating method. Sprayingmethod is a method in which the anode active material is sprayed in afused state or a semi-fused state. Firing method is, for example, amethod in which after the anode current collector is coated by aprocedure similar to that of coating method, heat treatment is providedat temperature higher than the melting point of the anode binder or thelike. Examples of firing methods include a known technique such asatmosphere firing method, reactive firing method, and hot press firingmethod.

The anode active material is composed of, for example, a plurality ofparticles. In this case, the anode active material layer 22B contains aplurality of particulate anode active materials (hereinafter referred toas “anode active material particles”). The anode active materialparticles in the case where coating method or the like is used as amethod of forming the anode active material layer 22B is particulateanode active material itself used for preparing coating-use slurry.Meanwhile, the anode active material particles in the case wherevapor-phase deposition method, spraying method or the like is used as amethod of forming the anode active material layer 22B is an anode activematerial that becomes in a state of particles as a result of beingdeposited on the anode current collector 22A due to evaporation, meltingor the like.

In the case where the anode active material particles are formed byusing a deposition method such as vapor-phase deposition method, theanode active material particles may have a single layer structure formedby a single deposition step or may have a multilayer structure formed bya plurality of deposition steps. However, in the case where evaporationmethod or the like associated with high heat is used at the time ofdeposition, the anode active material particles preferably have amultilayer structure. In this case, the deposition step of the anodematerial is divided into several steps (a plurality of thin layers ofthe anode material are sequentially formed and deposited). Thus, timethat the anode current collector 22A is exposed at high heat isshortened compared to a case that the deposition is performed in asingle deposition step. Thereby, the anode current collector 22A is lesslikely to be subject to thermal damage.

The anode active material particles are preferably grown, for example,in the thickness direction of the anode active material layer 22B fromthe surface of the anode current collector 22A, and the anode activematerial particles are preferably linked to the anode current collector22A at the root thereof. Thereby, expansion and shrinkage of the anodeactive material layer 22B are inhibited at the time of charge anddischarge. Further, the anode active material particles are preferablyformed by vapor-phase deposition method, liquid-phase deposition method,firing method or the like, and at least part of the interface with theanode current collector 22A is preferably alloyed. In this case, at theinterface therebetween, the constituent element of the anode currentcollector 22A may be diffused in the anode active material particles; orthe constituent element of the anode active material particles may bediffused in the anode current collector 22A; or the respectiveconstituent elements may be diffused in each other.

In particular, the anode active material layer 22B preferably containsan oxide-containing film to cover the surface of the anode activematerial particles (region to be contacted with the electrolyte if theoxide-containing film is not provided) according to needs. In this case,the oxide-containing film functions as a protective film for theelectrolyte, and accordingly decomposition reaction of the electrolyteis inhibited at the time of charge and discharge. Thereby, cyclecharacteristics, storage characteristics and the like are improved. Inaddition, the oxide-containing film may cover the entire surface of theanode active material particles, or may cover only part thereof.Specially, the oxide-containing film preferably covers the entiresurface of the anode active material particles, since therebydecomposition reaction of the electrolyte is more inhibited.

The oxide-containing film contains, for example, at least one kind of asilicon oxide, a germanium oxide, and a tin oxide. Specially, theoxide-containing film preferably contains the silicon oxide, sincethereby the oxide-containing film easily covers the entire surface ofthe anode active material particles, and superior protective action isable to be thereby obtained. It is needless to say that theoxide-containing film may contain an oxide other than the foregoingoxides.

The oxide-containing film is formed by, for example, vapor-phasedeposition method, liquid-phase deposition method or the like.Specially, the oxide-containing film is preferably formed byliquid-phase deposition method, since thereby the oxide-containing filmeasily covers a wide range of the surface of the anode active materialparticles. Examples of liquid-phase deposition methods includeliquid-phase precipitation method, sol gel method, coating method, anddip coating method. Specially, liquid-phase precipitation method, solgel method, or dip coating method is preferable, and liquid-phaseprecipitation method is more preferable, since thereby higher effect isobtained. It is to be noted that the oxide-containing film may be formedby a single formation method of the foregoing formation methods, or maybe formed by two or more formation methods thereof.

Further, the anode active material layer 22B preferably contains a metalmaterial containing a metal element not being alloyed with lithium as aconstituent element (hereinafter simply referred to as “metal material”)in a gap inside the anode active material layer 22B according to needs.Thereby, the plurality of anode active materials are bound to each otherwith the metal material in between. In addition, since the void ratio inthe anode active material layer 22B is decreased, expansion andshrinkage of the anode active material layer 22B are inhibited. Thereby,cycle characteristics, storage characteristics and the like areimproved. For the details of “gap inside the anode active material layer22B,” a description will be given later (refer to FIGS. 5 and 6).

Examples of the foregoing metal elements include at least one kindselected from the group consisting of iron, cobalt, nickel, zinc, andcopper. Specially, cobalt is preferable, since thereby the metalmaterial easily intrudes into the gap inside the anode active materiallayer 22B, and superior binding characteristics are obtained. It isneedless to say that the metal element may be a metal element other thanthe foregoing metal elements. However, “metal material” herein is acomprehensive term, including not only a simple substance but also analloy and a metal compound.

The metal material is formed by, for example, vapor-phase depositionmethod, liquid-phase deposition method or the like. Specially, the metalmaterial is preferably formed by liquid-phase deposition method, sincethereby the metal material easily intrudes into the gap inside the anodeactive material layer 22B. Examples of liquid-phase deposition methodsinclude electrolytic plating method and electroless plating method.Specially, electrolytic plating method is preferable, since thereby themetal material more easily intrudes into the foregoing gap, and theformation time thereof is shortened. In addition, the metal material maybe formed by a single formation method out of the foregoing formationmethods, or may be formed by two or more formation methods thereof.

In addition, the anode active material layer 22B may contain only one ofthe oxide-containing film and the metal material, or may contain boththereof. However, in order to further improve cycle characteristics andthe like, the anode active material layer 22B preferably contains boththereof. In the case where the anode active material layer 22B containsonly one thereof, in order to further improve cycle characteristics andthe like, the anode active material layer 22B preferably contains theoxide-containing film. In addition, in the case where the anode activematerial layer 22B contains both the oxide-containing film and the metalmaterial, any thereof may be formed firstly. However, in order tofurther improve cycle characteristics and the like, the oxide-containingfilm is preferably formed first.

A description will be given of a detailed structure of the anode 22 withreference to FIG. 3 to FIG. 6.

First, a description will be given of a case that the anode activematerial layer 22B contains the plurality of anode active materialparticles and the oxide-containing film. FIG. 3 and FIG. 4 schematicallyillustrate a cross sectional structure of the anode 22. In this case, acase that the anode active material particles have a single layerstructure is illustrated.

In the case illustrated in FIG. 3, for example, if the anode material isdeposited on the anode current collector 22A by vapor-phase depositionmethod such as evaporation method, a plurality of anode active materialparticles 221 are formed on the anode current collector 22A. In thiscase, if the surface of the anode current collector 22A is roughened anda plurality of projection sections (for example, fine particles formedby electrolytic treatment) exist on the surface, the anode activematerial particles 221 are grown for every projection section in thethickness direction. Thus, the plurality of anode active materialparticles 221 are arranged on the anode current collector 22A, and arelinked to the anode current collector 22A at the root thereof. Afterthat, for example, an oxide-containing film 222 is formed on the surfaceof the anode active material particles 221 by liquid-phase depositionmethod such as liquid-phase precipitation method. The oxide-containingfilm 222 covers almost entire surface of the anode active materialparticles 221. In this case, a wide range from the top of the anodeactive material particles 221 to the root thereof is covered. Such awide range covering state is characteristic obtained in the case wherethe oxide-containing film 222 is formed by liquid-phase depositionmethod. That is, in the case where the oxide containing film 222 isformed by liquid-phase deposition method, covering action is applied notonly to the top of the anode active material particles 221 but also tothe root thereof, and thus the oxide-containing film 222 covers aportion from the top of the anode active material particles 221 to theroot thereof.

Meanwhile, in the case illustrated in FIG. 4, for example, after theplurality of anode active material particles 221 are formed byvapor-phase deposition method, an oxide-containing film 223 is formedsimilarly by vapor-phase deposition method. The oxide-containing film223 covers only part (the top) of the anode active material particles221. Such a small range covering state is characteristic obtained in thecase where the oxide-containing film 223 is formed by vapor-phasedeposition method. That is, in the case where the oxide containing film223 is formed by using vapor-phase deposition method, covering action isapplied to the top of the anode active material particles 221 but notapplied to the root thereof, and thus the oxide-containing film 223 doesnot cover the root thereof.

In addition, FIG. 3 illustrates the case that the anode active materiallayer 22B is formed by vapor-phase deposition method. However, the sameresult is also applied if the anode active material layer 22B is formedby other formation method such as coating method and sintering method.That is, the oxide-containing film 222 is formed to cover almost entiresurface of the plurality of anode active material particles.

Next, a description will be given of a case that the anode activematerial layer 22B contains the metal material together with theplurality of anode active material particles. FIGS. 5 and 6 illustratean enlarged cross sectional structure of the anode 22. In FIGS. 5 and 6,(A) illustrates a Scanning Electron Microscope (SEM) photograph(secondary electron image), and (B) illustrates a schematic drawing ofthe SEM image illustrated in (A) of FIGS. 5 and 6. In this case, FIGS. 5and 6 illustrate a case that the plurality of anode active materialparticles 221 have a multilayer structure.

As illustrated in FIG. 5, in the case where the anode active materialparticles 221 have the multilayer structure, a plurality of gaps 224 aregenerated in the anode active material layer 22B due to the arrangementstructure, the multilayer structure, and the surface structure of theanode active material particles 221. The gap 224 mainly includes twotypes of gaps 224A and 224B categorized according to the cause ofgeneration. The gap 224A is a gap generated between the anode activematerial particles 221. Meanwhile, the gap 224B is a gap generatedbetween each layer in the anode active material particles 221. However,the gap 224 generated by other generation cause may exist.

In addition, on the exposed face (outermost surface) of the anode activematerial particle 221, a void 225 is generated in some cases. As afibrous minute projection section (not illustrated) is formed on thesurface of the anode active material particles 221, the void 225 isgenerated between the projection sections. The void 225 may be generatedentirely over the exposed face of the anode active material particles221, or may be generated in only part thereof. However, since thefibrous projection section is generated on the surface of the anodeactive material particles 221 every time the anode active materialparticle 221 is formed, the void 225 is generated between each layer inaddition to on the exposed face of the anode active material particles221 in some cases.

As illustrated in FIG. 6, the anode active material layer 22B has ametal material 226 in the gaps 224A and 224B. In this case, though onlyone of the gaps 224A and 224B may have the metal material 226, both thegaps 224A and 224B preferably have the metal material 226, since therebyhigher effect is obtained.

The metal material 226 intrudes into the gap 224A between the anodeactive material particles 221. More specifically, in the case where theanode active material particles 221 are formed by vapor-phase depositionmethod or the like, the anode active material particles 221 are grownfor every projection section existing on the surface of the anodecurrent collector 22A as described above, and thus the gap 224A isgenerated between the anode active material particles 221. The gap 224Acauses lowering of the binding characteristics of the anode activematerial layer 22B. Therefore, to improve the binding characteristics,the metal material 226 fills in the gap 224A. In this case, it is enoughthat part of the gap 224A is filled therewith, but the larger fillingamount is preferable, since thereby the binding characteristics of theanode active material layer 22B are more improved. The filling amount ofthe metal material 226 is preferably 20% or more, more preferably 40% ormore, and much more preferably 80% or more.

Further, the metal material 226 intrudes into the gap 224B in the anodeactive material particles 221. More specifically, in the case where theanode active material particles 221 have a multilayer structure, the gap224B is generated between each layer.

The gap 224B causes lowering of the binding characteristics of the anodeactive material layer 22B as the gap 224A does. Therefore, to improvethe binding characteristics, the metal material 226 fills in the gap224B. In this case, it is enough that part of the gap 224B is filledtherewith, but the larger filling amount is preferable, since therebythe binding characteristics of the anode active material layer 22B aremore improved.

In addition, to prevent the fibrous minute projection section (notillustrated) generated on the exposed face of the uppermost layer of theanode active material particles 221 from adversely affecting theperformance of the secondary battery, the anode active material layer22B may have the metal material 226 in the void 225. More specifically,in the case where the anode active material particles 221 are formed byvapor-phase deposition method or the like, the fibrous minute projectionsections are generated on the surface thereof, and thus the void 225 isgenerated between the projection sections. The void 225 causes increaseof the surface area of the anode active material particles 221, andaccordingly the amount of an irreversible coat formed on the surface isalso increased, possibly resulting in lowering of progression of chargeand discharge reaction. Therefore, to inhibit the lowering ofprogression of the charge and discharge reaction, the void 225 is filledwith the metal material 226. In this case, it is enough at minimum thatpart of the void 225 is filled therewith, but the larger filling amountis preferable, since thereby lowering of progression of the charge anddischarge reaction is more inhibited. In FIG. 6, the metal material 226is scattered about the surface of the uppermost layer of the anodeactive material particles 221, which means that the foregoing minuteprojection section exists in the location where the metal material 226is scattered. It is needless to say that the metal material 226 is notnecessarily scattered about the surface of the anode active materialparticles 221, but may cover the entire surface thereof.

In particular, the metal material 226 that intrudes into the gap 224Bhas a function to fill in the void 225 in each layer. More specifically,in the case where the anode material is deposited several times, theminute projection section is generated on the surface of the anodeactive material particles 221 for every deposition. Therefore, the metalmaterial 226 fills in not only the gap 224B in each layer, but also thevoid 225 in each layer.

It is to be noted that in FIGS. 5 and 6, the description has been givenof the case that the anode active material particles 221 have themultilayer structure, and both gaps 224A and 224B exist in the anodeactive material layer 22B. Thus, the anode active material layer 22B hasthe metal material 226 in the gaps 224A and 224B. Meanwhile, in the casewhere the anode active material particles 221 have a single layerstructure, and only the gap 224A exists in the anode active materiallayer 22B, the anode active material layer 22B has the metal material226 only in the gap 224A. It is needless to say that the void 225 isgenerated in both cases, and thus in any case, the metal material 226 isincluded in the void 225.

[Separator]

The separator 23 separates the cathode 21 from the anode 22, and passeslithium ions while preventing current short circuit resulting fromcontact of both electrodes. The separator 23 is impregnated with theforegoing electrolyte as a liquid electrolyte (electrolytic solution).The separator 23 is made of, for example, a porous film composed of asynthetic resin or ceramics. The separator 23 may be a laminated bodycomposed of two or more kinds of porous films. The synthetic resin is,for example, polytetrafluoroethylene, polypropylene, polyethylene or thelike.

[Operation of Secondary Battery]

In the secondary battery, at the time of charge, for example, lithiumions are extracted from the cathode 21, and are inserted in the anode 22through the electrolytic solution with which the separator 23 isimpregnated. Meanwhile, at the time of discharge, for example, lithiumions are extracted from the anode 22, and are inserted in the cathode 21through the electrolytic solution with which the separator 23 isimpregnated.

[Method of Manufacturing Secondary Battery]

The secondary battery is manufactured, for example, by the followingprocedure.

First, the cathode 21 is formed. First, a cathode active material ismixed with a cathode binder, a cathode electrical conductor or the likeaccording to needs to prepare a cathode mixture, which is subsequentlydispersed in an organic solvent to obtain paste cathode mixture slurry.Subsequently, both faces of the cathode current collector 21A areuniformly coated with the cathode mixture slurry, which is dried to formthe cathode active material layer 21B. Finally, the cathode activematerial layer 21B is compression-molded by using a rolling pressmachine or the like while being heated if necessary. In this case, theresultant may be compression-molded over several times.

Next, the anode 22 is formed by a procedure similar to that of theforegoing cathode 21. In this case, an anode active material is mixedwith an anode binder, an anode electrical conductor or the likeaccording to needs to prepare an anode mixture, which is subsequentlydispersed in an organic solvent to form paste anode mixture slurry.After that, both faces of the anode current collector 22A are uniformlycoated with the anode mixture slurry to form the anode active materiallayer 22B. After that, the anode active material layer 22B iscompression-molded.

In addition, the anode 22 may be formed by a procedure different fromthat of the cathode 21. In this case, first, the anode material isdeposited on both faces of the anode current collector 22A by usingvapor-phase deposition method such as evaporation method to form aplurality of anode active material particles. After that, according toneeds, an oxide-containing film is formed by using liquid-phasedeposition method such as liquid-phase precipitation method, or a metalmaterial is formed by using liquid-phase deposition method such aselectrolytic plating method, or both the oxide-containing film and themetal material are formed to form the anode active material layer 22B.

Finally, the secondary battery is assembled by using the cathode 21 andthe anode 22. First, the cathode lead 25 is attached to the cathodecurrent collector 21A by welding or the like, and the anode lead 26 isattached to the anode current collector 22A by welding or the like.Subsequently, the cathode 21 and the anode 22 are layered with theseparator 23 in between and spirally wound, and thereby the spirallywound electrode body 20 is formed. After that, the center pin 24 isinserted in the center of the spirally wound electrode body 20.Subsequently, the spirally wound electrode body 20 is sandwiched betweenthe pair of insulating plates 12 and 13, and is contained in the batterycan 11. In this case, the end of the cathode lead 25 is attached to thesafety valve mechanism 15 by welding or the like, and the end of theanode lead 26 is attached to the battery can 11 by welding or the like.Subsequently, the electrolytic solution is injected into the battery can11 and the separator 23 is impregnated with the electrolytic solution.Finally, at the open end of the battery can 11, the battery cover 14,safety valve mechanism 15, and the PTC device 16 are fixed by beingcaulked with the gasket 17. The secondary battery illustrated in FIG. 1to FIG. 6 is thereby completed.

According to the first secondary battery, in the case where the capacityof the anode 22 is expressed by insertion and extraction of lithium ion,the foregoing electrolyte (electrolytic solution) is included. Thus,decomposition reaction of the electrolytic solution at the time ofcharge and discharge is inhibited, and accordingly cycle characteristicsare able to be improved. In addition, even if being exposed under hightemperature environment in charged state, the foregoing electrolyticsolution is hardly decomposed, and thus gasification of decomposedelectrolytic solution is inhibited. Accordingly, operation time of thesafety valve due to pressure increase inside the secondary battery underhigh temperature environment is increased, and accordingly safety isable to be improved.

In particular, in the case where the metal material advantageous torealizing a high capacity as an anode active material of the anode 22 isused, cycle characteristics are improved. Thus, higher effect is able tobe obtained than in a case that a carbon material or the like is used.

Other effect for the first secondary battery is similar to that of theforegoing electrolyte.

<2-2. Second Secondary Battery>

[Structure of Secondary Battery]

A second secondary battery is a lithium metal secondary battery in whichthe anode capacity is expressed by precipitation and dissolution oflithium metal. The secondary battery has a structure similar to that ofthe first secondary battery, except that the anode active material layer22B is composed of lithium metal, and is manufactured by a proceduresimilar to that of the first secondary battery.

In the secondary battery, lithium metal is used as an anode activematerial, and thereby a higher energy density is able to be obtained. Itis possible that the anode active material layer 22B already exists atthe time of assembling, or the anode active material layer 22B does notexist at the time of assembling and is to be composed of lithium metalto be precipitated at the time of charge. Further, it is possible thatthe anode active material layer 22B is used as a current collector aswell, and the anode current collector 22A is omitted.

[Operation of Secondary Battery]

In the secondary battery, when charged, for example, lithium ions areextracted from the cathode 21, and are precipitated as lithium metal onthe surface of the anode current collector 22A through the electrolyticsolution with which the separator 23 is impregnated. Meanwhile, whendischarged, for example, lithium metal is eluted as lithium ions fromthe anode active material layer 22B, and is inserted in the cathode 21through the electrolytic solution with which the separator 23 isimpregnated.

According to the second secondary battery, in the case where thecapacity of the anode 22 is expressed by precipitation and dissolutionof lithium metal, the foregoing electrolyte (electrolytic solution) isincluded. Thus, cycle characteristics are able to be improved by anaction similar to that of the first secondary battery. Other effect ofthe secondary battery is similar to that of the first secondary battery.

<2-3. Third Secondary Battery>

FIG. 7 illustrates an exploded perspective structure of a thirdsecondary battery. FIG. 8 illustrates an enlarged cross section takenalong line VIII-VIII of a spirally wound electrode body 30 illustratedin FIG. 7.

[Whole Structure of Secondary Battery]

The secondary battery is a lithium ion secondary battery as in the firstsecondary battery. In the secondary battery, the spirally woundelectrode body 30 on which a cathode lead 31 and an anode lead 32 areattached is contained in a film package member 40 mainly. The batterystructure using such a package member 40 is called the laminated filmtype.

The cathode lead 31 and the anode lead 32 are respectively led out frominside to outside of the package member 40 in the same direction, forexample. However, arrangement positions of the cathode lead 31 and theanode lead 32 with respect to the spirally wound electrode body 30,derivation directions thereof and the like are not particularly limited.The cathode lead 31 is made of, for example, aluminum or the like, andthe anode lead 32 is made of, for example, copper, nickel, stainless orthe like. These materials are in the shape of, for example, a thin plateor mesh.

[Package Member]

The package member 40 is made of a laminated film in which, for example,a fusion bonding layer, a metal layer, and a surface protective layerare layered in this order. In this case, for example, the respectiveouter edges of the fusion bonding layer of two films are bonded to eachother by fusion bonding, an adhesive or the like so that the fusionbonding layer and the spirally wound electrode body 30 are opposed toeach other. Examples of the fusion bonding layer include a film made ofpolyethylene, polypropylene or the like. Examples of the metal layerinclude an aluminum foil. Examples of the surface protective layerinclude a film made of nylon, polyethylene terephthalate or the like.

Specially, as the package member 40, an aluminum laminated film in whicha polyethylene film, an aluminum foil, and a nylon film are layered inthis order is preferable. However, the package member 40 may be made ofa laminated film having other laminated structure, a polymer film suchas polypropylene, or a metal film, instead of the aluminum laminatedfilm.

An adhesive film 41 to protect from entering of outside air is insertedbetween the package member 40 and the cathode lead 31, the anode lead32. The adhesive film 41 is made of a material having contactcharacteristics with respect to the cathode lead 31 and the anode lead32. Examples of such a material include, for example, a polyolefin resinsuch as polyethylene, polypropylene, modified polyethylene, and modifiedpolypropylene.

[Cathode, Anode, and Separator]

In the spirally wound electrode body 30, a cathode 33 and an anode 34are layered with a separator 35 and an electrolyte layer 36 in betweenand spirally wound. The outermost periphery thereof is protected by aprotective tape 37. The cathode 33 has a structure in which, forexample, a cathode active material layer 33B is provided on both facesof a cathode current collector 33A. The structures of the cathodecurrent collector 33A and the cathode active material layer 33B arerespectively similar to those of the cathode current collector 21A andthe cathode active material layer 21B in the first secondary battery.The anode 34 has a structure in which, for example, an anode activematerial layer 34B is provided on both faces of an anode currentcollector 34A. The structures of the anode current collector 34A and theanode active material layer 34B are respectively similar to thestructures of the anode current collector 22A and the anode activematerial layer 22B in the first secondary battery.

In addition, the structure of the separator 35 is similar to thestructure of the separator 23 in the first secondary battery.

[Electrolyte Layer]

In the electrolyte layer 36, an electrolytic solution is held by apolymer compound, and other material such as various additives may becontained according to needs. The electrolyte layer 36 is a so-calledgel electrolyte. The gel electrolyte is preferable, since high ionconductivity (for example, 1 mS/cm or more at room temperature) isobtained and liquid leakage of the electrolytic solution is prevented.

Examples of the polymer compound include at least one of the followingpolymer materials. That is, examples thereof include polyacrylonitrile,polyvinylidene fluoride, polytetrafluoroethylene,polyhexafluoropropylene, polyethylene oxide, polypropylene oxide,polyphosphazene, polysiloxane, and polyvinyl fluoride. Further, examplesthereof include polyvinyl acetate, polyvinyl alcohol, polymethacrylicacid methyl, polyacrylic acid, polymethacrylic acid, styrene-butadienerubber, nitrile-butadiene rubber, polystyrene, and polycarbonate.Further, examples thereof include a copolymer of vinylidene fluoride andhexafluoropropylene. One of these polymer compounds may be used singly,or a plurality thereof may be used by mixture. Specially, polyvinylidenefluoride or the copolymer of vinylidene fluoride and hexafluoropropyleneis preferable, since such a polymer compound is electrochemicallystable.

The composition of the electrolytic solution is similar to thecomposition of the electrolytic solution in the first secondary battery.However, in the electrolyte layer 36 as the gel electrolyte, a solventof the electrolytic solution means a wide concept including not only theliquid solvent but also a solvent having ion conductivity capable ofdissociating the electrolyte salt. Therefore, in the case where thepolymer compound having ion conductivity is used, the polymer compoundis also included in the solvent.

In addition, instead of the gel electrolyte layer 36 in which theelectrolytic solution is held by the polymer compound, the electrolyticsolution may be directly used. In this case, the separator 35 isimpregnated with the electrolytic solution.

[Operation of Secondary Battery]

In the secondary battery, at the time of charge, for example, lithiumions are extracted from the cathode 33, and are inserted in the anode 34through the electrolyte layer 36. Meanwhile, at the time of discharge,for example, lithium ions are extracted from the anode 34, and areinserted in the cathode 33 through the electrolyte layer 36.

[Manufacturing Method of Secondary Battery]

The secondary battery including the gel electrolyte layer 36 ismanufactured, for example, by the following three procedures.

In the first manufacturing method, first, the cathode 33 and the anode34 are formed by a procedure similar to that of the cathode 21 and theanode 22 in the first secondary battery. Specifically, the cathode 33 isformed by forming the cathode active material layer 33B on both faces ofthe cathode current collector 33A, and the anode 34 is formed by formingthe anode active material layer 34B on both faces of the anode currentcollector 34A. Subsequently, a precursor solution containing anelectrolytic solution, a polymer compound, and a solvent is prepared.After the cathode 33 and the anode 34 are coated with the precursorsolution, the solvent is volatilized to form the gel electrolyte layer36, Subsequently, the cathode lead 31 is attached to the cathode currentcollector 33A by welding or the like, and the anode lead 32 is attachedto the anode current collector 34A by welding or the like. Subsequently,the cathode 33 and the anode 34 provided with the electrolyte layer 36are layered with the separator 35 in between and spirally wound toobtain a laminated body. After that, a protective tape 37 is adhered tothe outermost periphery thereof to form the spirally wound electrodebody 30. Finally, after the spirally wound electrode body 30 issandwiched between two pieces of film-like package members 40, outeredges of the package members 40 are bonded by thermal fusion bonding orthe like to enclose the spirally wound electrode body 30. At this time,the adhesive films 41 are inserted between the cathode lead 31, theanode lead 32 and the package member 40. Thereby, the secondary batteryillustrated in FIG. 7 and FIG. 8 is completed.

In the second manufacturing method, first, the cathode lead 31 isattached to the cathode 33, and the anode lead 32 is attached to theanode 34. Subsequently, the cathode 33 and the anode 34 are layered withthe separator 35 in between and spirally wound. After that, theprotective tape 37 is adhered to the outermost periphery thereof, andthereby a spirally wound body as a precursor of the spirally woundelectrode body 30 is formed. Subsequently, after the spirally wound bodyis sandwiched between two pieces of the film-like package members 40,the outermost peripheries except for one side are bonded by thermalfusion bonding or the like to obtain a pouched state, and the spirallywound body is contained in the pouch-like package member 40.Subsequently, a composition of matter for electrolyte containing anelectrolytic solution, a monomer as a raw material for the polymercompound, a polymerization initiator, and if necessary other materialsuch as a polymerization inhibitor is prepared, which is injected intothe pouch-like package member 40. After that, the opening of the packagemember 40 is hermetically sealed by thermal fusion bonding or the like.Finally, the monomer is thermally polymerized to obtain a polymercompound. Thereby, the gel electrolyte layer 36 is formed. Accordingly,the secondary battery is completed.

In the third manufacturing method, the spirally wound body is formed andcontained in the pouch-like package member 40 in the same manner as thatof the foregoing second manufacturing method, except that the separator35 with both faces coated with a polymer compound is used firstly.Examples of the polymer compound with which the separator 35 is coatedinclude a polymer containing vinylidene fluoride as a component (ahomopolymer, a copolymer, a multicomponent copolymer or the like).Specific examples thereof include polyvinylidene fluoride, a binarycopolymer containing vinylidene fluoride and hexafluoropropylene as acomponent, and a ternary copolymer containing vinylidene fluoride,hexafluoropropylene, and chlorotrifluoroethylene as a component. Inaddition, as a polymer compound, in addition to the foregoing polymercontaining vinylidene fluoride as a component, another one or more kindsof polymer compounds may be contained. Subsequently, an electrolyticsolution is prepared and injected into the package member 40. Afterthat, the opening of the package member 40 is sealed by thermal fusionbonding or the like. Finally, the resultant is heated while a weight isapplied to the package member 40, and the separator 35 is contacted withthe cathode 33 and the anode 34 with the polymer compound in between.Thereby, the polymer compound is impregnated with the electrolyticsolution, and the polymer compound is gelated to form the electrolytelayer 36, Accordingly, the secondary battery is completed.

In the third manufacturing method, the battery swollenness is inhibitedmore than in the first manufacturing method. Further, in the thirdmanufacturing method, the monomer, the solvent and the like as a rawmaterial of the polymer compound are hardly left in the electrolytelayer 36 compared to in the second manufacturing method. In addition,the formation step of the polymer compound is favorably controlled.Thus, sufficient contact characteristics are obtained between thecathode 33/the anode 34/the separator 35 and the electrolyte layer 36.

According to the third secondary battery, in the case where the capacityof the anode 34 is expressed by insertion and extraction of lithiumions, the electrolyte layer 36 contains the foregoing electrolyte(electrolytic solution). Thus, cycle characteristics are able to beimproved by an action similar to that of the first secondary battery.Other effect of the secondary battery is similar to that of the firstsecondary battery. It is to be noted that the structure of the thirdsecondary battery is not limited to the structure similar to that of thefirst secondary battery, and may be a structure similar to that of thesecond secondary battery. In the latter case, similar effect is able tobe also obtained.

EXAMPLES

Specific examples of the present invention will be described in detail.

Examples 1-1 to 1-32

The cylindrical type lithium ion secondary batteries illustrated in FIG.1 and FIG. 2 were fabricated by the following procedure.

First, the cathode 21 was formed. In this case, first, lithium carbonate(Li₂CO₃) and cobalt carbonate (CoCO₃) were mixed at a molar ratio of0.5:1. After that, the mixture was fired in the air at 900 deg C. for 5hours. Thereby, lithium-cobalt composite oxide (LiCoO₂) was obtained.Subsequently, 91 parts by mass of LiCoO₂ as a cathode active material, 6parts by mass of graphite as a cathode electrical conductor, and 3 partsby mass of polyvinylidene fluoride as a cathode binder were mixed toobtain a cathode mixture. Subsequently, the cathode mixture wasdispersed in N-methyl-2-pyrrolidone to obtain paste cathode mixtureslurry. Subsequently, both faces of the cathode current collector 21Awere uniformly coated with the cathode mixture slurry by using a coatingdevice, which was dried to form the cathode active material layer 21B.As the cathode current collector 21A, a strip-shaped aluminum foil(thickness: 12 μm) was used. Finally, the cathode active material layer21B was compression-molded by using a roll pressing machine.

Next, the anode 22 was formed. In this case, first, 97 parts by mass ofartificial graphite as an anode active material and 3 parts by mass ofpolyvinylidene fluoride as an anode binder were mixed to obtain an anodemixture. Subsequently, the anode mixture was dispersed inN-methyl-2-pyrrolidone to obtain paste anode mixture slurry.Subsequently, both faces of the anode current collector 22A wereuniformly coated with the anode mixture slurry by using a coatingdevice, which was dried to form the anode active material layer 22B. Asthe anode current collector 22A, a strip-shaped electrolytic copper foil(thickness: 15 μm) was used. Finally, the anode active material layer22B (single face thickness: 70 μm) was compression-molded by using aroll pressing machine.

Next, an electrolytic solution as a liquid electrolyte was prepared. Inthis case, first, as a solvent, ethylene carbonate (EC) and dimethylcarbonate (DMC) were mixed at a weight ratio of EC:DMC=30:70.Subsequently, lithium hexafluorophosphate (LiPF₆) as an electrolyte saltwas added and dissolved into the mixed solvent so that the content oflithium hexafluorophosphate was 1.2 mol/kg. Finally, a sulfone compoundand a nitrile compound or the like were added and were subsequentlymixed. At this time, as the sulfone compound, the compound shown inFormula (1-1) or the compound shown in Formula (1-2) was used. Further,as the nitrile compound, succinonitrile (SCN), 1,6-dicyanohexane (DCNH),1,2,3-propane tricarbonitrile (PTCN), or7,7,8,8-tetracyanoquinodimethane (TCNQ) was used. As the isocyanatecompound, 1-isocyanato pentane (NCOP), 1,8-dicyanato octane (DNCO), or1,4-diisocyanato butane-1,4-dione (DNCOB) was used. As the pyrrolidonecompound, N-ethyl-2-pyrrolidone (NEP), N-propyl-2-pyrrolidone (NPP),N-cyclohexyl-2-pyrrolidone (NCHP), or N-phenyl-2-pyrrolidone (NPhP) wasused. As the ether compound, NOVEC HFE7100 (manufactured by 3M Company)as C₄F₉OCH₃ or NOVEC HFE7300 (manufactured by 3M Company) as C₆F₁₃OCH₃was used. The content of the sulfone compound and the content of thenitrile compound or the like (except for the ether compound) in theelectrolytic solution of respective examples (weight %: wt %) were asillustrated in Table 1 and Table 2. However, in Examples 1-12, 1-13,1-25, 1-26, and 1-30 to 1-32 using the ether compound, the electrolyticsolution was prepared in the same manner as the foregoing manner, exceptthat a mixed solvent obtained by mixing EC, DMC, and the ether compoundat a weight ratio of EC:DMC:ether compound=30:60:10.

Finally, the secondary battery was assembled by using the cathode 21,the anode 22, and the electrolytic solution. In this case, first, thecathode lead 25 was welded to the cathode current collector 21A, and theanode lead 26 was welded to the anode current collector 22A.Subsequently, the cathode 21 and the anode 22 were layered with theseparator 23 in between and spirally wound to form the spirally woundelectrode body 20. After that, the center pin 24 was inserted in thecenter of the spirally wound electrode body 20. As the separator 23, amicroporous polypropylene film (thickness: 25 μm) was used.Subsequently, while the spirally wound electrode body 20 was sandwichedbetween the pair of insulating plates 12 and 13, the spirally woundelectrode body 20 was contained in the battery can 11 made of ironplated with nickel. At this time, the cathode lead 25 was welded to thesafety valve mechanism 15, and the anode lead 26 was welded to thebattery can 11. Subsequently, with the use of depressurization method,the electrolytic solution was injected into the battery can 11, and theseparator 23 was impregnated with the electrolytic solution. Finally, atthe open end of the battery can 11, the battery cover 14, safety valvemechanism 15, and the PTC device 16 were fixed by being caulked with thegasket 17. The cylindrical type secondary battery was thereby completed.In forming the secondary battery, lithium metal was prevented from beingprecipitated on the anode 22 at the full charged state by adjusting thethickness of the cathode active material layer 21B.

Examples 1-33 to 1-48

A procedure similar to that of Examples 1-1 to 1-32 was executed, exceptthat combination of the sulfone compound and the nitrile compound or thelike was not used as illustrated in Table 2. However, in Examples 1-47and 1-48 in which the ether compound was used, a mixed solvent obtainedby mixing EC, DMC, and the ether compound at a weight ratio ofEC:DMC:ether compound=30:60:10 was used.

Cycle characteristics and safety respectively at 23 deg C. and 45 deg C.for the secondary batteries of Examples 1-1 to 1-48 were examined. Theresults illustrated in Table 1 and Table 2 were obtained.

In examining cycle characteristics at 23 deg C., first, 2 cycles ofcharge and discharge were performed in the atmosphere at 23 deg C., andthe discharge capacity at the second cycle was measured. Subsequently,the secondary battery was charged and discharged repeatedly in the sameatmosphere until the total number of cycles became 200 cycles, andthereby the discharge capacity at the 200th cycle was measured. Finally,the cycle discharge capacity retention ratio (%)=(discharge capacity atthe 200th cycle/discharge capacity at the second cycle)*100 wascalculated. At the time of charge, constant current and constant voltagecharge was performed at a constant current density of 1 mA/cm² until theupper voltage of 4.2 V, and charge was performed at a constant voltageof 4.2 V until a current density of 0.02 mA/cm². At the time ofdischarge, constant current discharge was performed at a constantcurrent density of 1 mA/cm² until the final voltage of 3.0 V.

In examining cycle characteristics at 45 deg C., the cycle dischargecapacity retention ratio was calculated in the same manner as that ofcycle characteristics at 23 deg C., except that atmosphere at the timeof charge and discharge was 45 deg C.

In examining safety, safety valve operation time was measured. In thiscase, first, 2 cycles of charge and discharge were performed in theatmosphere at 23 deg C. Subsequently, the battery that had been chargedagain was stored in a constant temperature bath at 95 deg C., and timeuntil safety valve mechanism 15 of the secondary battery staredoperation was measured. The charge and discharge conditions were similarto those in the case of examining cycle characteristics.

It is to be noted that the procedures and the conditions in examiningcycle characteristics at 23 deg C. and at 45 deg C. and safety asdescribed above were similarly applied to the following examples.

TABLE 1 Anode active material: artificial graphite Solvent: EC + DMCElectrolyte salt: LiPF₆ Other solvent Cycle discharge Safety Nitrilecompound capacity valve Sulfone compound or the like retention ratiooperation Content Content Ether (%) time Type (wt %) Type (wt %)compound 23 deg C. 45 deg C. (time) Example 1-1 Formula 1 SCN 0.1 — 8385 81 Example 1-2 (1-1) DCNH 0.1 79 83 77 Example 1-3 PTCN 0.1 83 83 78Example 1-4 TCNQ 0.1 82 81 77 Example 1-5 NCOP 0.1 79 84 75 Example 1-6DNCO 0.5 82 85 81 Example 1-7 DNCOB 0.5 81 85 78 Example 1-8 NEP 0.5 8182 80 Example 1-9 NEP 0.5 80 82 80 Example 1-10 NCHP 0.5 79 85 79Example 1-11 NPhP 0.5 78 85 80 Example 1-12 — — C₄F₉OCH₃ 78 84 81Example 1-13 — — C₆F₁₃OCH₃ 77 84 80 Example 1-14 Formula 1 SCN 0.1 — 8588 80 Example 1-15 (1-2) DCNH 0.1 82 81 77 Example 1-16 PTCN 0.1 80 8377 Example 1-17 TCNQ 0.1 83 83 78 Example 1-18 NCOP 0.1 80 83 76 Example1-19 DNCO 0.5 83 85 81 Example 1-20 DNCOB 0.5 84 85 79 Example 1-21 NEP0.5 84 88 82 Example 1-22 NPP 0.5 82 86 81 Example 1-23 NCHP 0.5 80 8580 Example 1-24 NPhP 0.5 79 85 80 Example 1-25 — — C₄F₉OCH₃ 80 86 81Example 1-26 — — C₆F₁₃OCH₃ 80 84 80

TABLE 2 Anode active material: artificial graphite Solvent: EC + DMCElectrolyte salt: LiPF₆ Other solvent Cycle discharge Safety Nitrilecompound capacity valve Sulfone compound or the like retention ratiooperation Content Content Ether (%) time Type (wt %) Type (wt %)compound 23 deg C. 45 deg C. (time) Example 1-27 Formula 1 SCN + DNCO0.1 + 0.5 — 86 89 85 Example 1-28 (1-2) SCN + NEP 0.1 + 0.5 86 90 84Example 1-29 DNCO + NEP 0.5 + 0.5 86 86 85 Example 1-30 SCN 0.1 C₄F₉OCH₃86 90 83 Example 1-31 DNCO 0.5 88 91 83 Example 1-32 NEP 0.5 86 90 83Example 1-33 — — — — — 61 63 54 Example 1-34 Formula 1 — — — 71 75 55(1-1) Example 1-35 Formula 1 72 76 56 (1-2) Example 1-36 — — SCN 0.1 5053 62 Example 1-37 DCNH 0.1 45 46 59 Example 1-38 PTCN 0.1 48 49 60Example 1-39 TCNQ 0.1 46 49 58 Example 1-40 NCOP 0.1 55 59 59 Example1-41 DNCO 0.5 45 47 61 Example 1-42 DNCOB 0.5 58 60 58 Example 1-43 NEP0.5 53 55 62 Example 1-44 NPP 0.5 50 52 61 Example 1-45 NCHP 0.5 52 5661 Example 1-46 NPhP 0.5 50 52 60 Example 1-47 — — C₄F₉OCH₃ 44 50 62Example 1-48 — — C₆F₁₃OCH₃ 47 52 61

As illustrated in Table 1 and Table 2, in the secondary battery usingartificial graphite as an anode active material, the following resultwas obtained. That is, in Examples 1-1 to 1-32 in which the combinationof the sulfone compound and the nitrile compound or the like was used,the cycle discharge capacity retention ratios at 23 deg C. and 45 deg C.were higher and safety valve operation time was longer than in Examples1-33 to 1-48 in which the combination of the sulfone compound and thenitrile compound or the like was not used.

The foregoing results showed the following fact in the electrolyte ofthe secondary battery. In the case where only the sulfone compound wasused out of the sulfone compound and the nitrile compound or the like,electrolyte decomposition reaction at the time of repeated charge anddischarge at 23 deg C. and 45 deg C. (at the time of charge anddischarge at 23 deg C. and 45 deg C.) was slightly inhibited, but wasnot sufficiently inhibited. Meanwhile, if only the nitrile compound orthe like was used, electrolyte decomposition reaction at the time ofrepeated charge and discharge at 23 deg C. and 45 deg C. was improved.However, in using the combination of the sulfone compound and thenitrile compound or the like that are not able to sufficiently inhibitelectrolyte decomposition reaction at the time of charge and dischargeat 23 deg C. and 45 deg C., due to synergetic effect thereof,electrolyte decomposition inhibition effect was significantlydemonstrated. In addition, in using the combination of the sulfonecompound and the nitrile compound or the like, electrolyte decompositionreaction in the case where the battery was stored at 95 deg C. in astate of being charged was more significantly inhibited due tosynergetic effect. That is, in the case where both the sulfone compoundand the nitrile compound or the like were used, chemical stability ofthe electrolyte was more improved than in the case that both thereofwere not used or the case that only one thereof was used.

Further, the cycle discharge capacity retention ratio at 23 deg C. and45 deg C. and safety valve operation time became favorable withoutdepending on the type of the sulfone compound and the type of thenitrile compound or the like. Specially, in the case where the pluralityof kinds of nitrile compounds were used together with the sulfonecompound, the cycle discharge capacity retention ratio at 23 deg C. and45 deg C. and safety valve operation time became more favorable than inthe case that one kind of nitrile compound was used (refer to Examples1-14 to 1-32).

Accordingly, in the secondary battery using the artificial graphite asan anode active material, the following was confirmed. That is, in thecase where the solvent of the electrolyte contained at least one kind ofthe sulfone compounds and at least one kind of the nitrile compound, theisocyanate compound, the pyrrolidone compound, and the ether compound,cycle characteristics and safety were improved.

Examples 2-1 to 2-28

A procedure similar to that of Examples 1-1 to 1-13 and 1-34 wasexecuted, except that the compound shown in Formula (2-1) or thecompound shown in Formula (2-2) was used instead of the compound shownin Formula (1-1) as the sulfone compound as illustrated in Table 3. Forthe secondary batteries of Examples 2-1 to 2-28, cycle characteristicsat 23 deg C. and 45 deg C. and safety were examined. The resultsillustrated in Table 3 were obtained.

TABLE 3 Anode active material: artificial graphite Solvent EC + DMCElectrolyte salt: LiPF₆ Other solvent Safety Nitrile compound Cycledischarge valve Sulfone compound or the like capacity retentionoperation Content Content Ether ratio (%) time Type (wt %) Type (wt %)compound 23 deg C. 45 deg C. (time) Example 2-1 Formula 1 SCN 0.1 — 8183 79 Example 2-2 (2-1) DCNH 0.1 79 80 74 Example 2-3 PTCN 0.1 78 80 76Example 2-4 TCNQ 0.1 78 80 75 Example 2-5 NCOP 0.1 79 82 76 Example 2-6DNCO 0.5 80 83 78 Example 2-7 DNCOB 0.5 80 84 77 Example 2-8 NEP 0.5 7982 78 Example 2-9 NPP 0.5 79 82 77 Example 2-10 NCHP 0.5 78 80 75Example 2-11 NPhP 0.5 77 80 79 Example 2-12 — — C₄F₉OCH₃ 80 84 81Example 2-13 — — C₆F₁₃OCH₃ 79 83 80 Example 2-14 Formula 1 SCN 0.1 — 7983 79 Example 2-15 (2-2) DCNH 0.1 77 79 77 Example 2-16 PTCN 0.1 77 8075 Example 2-17 TCNQ 0.1 75 78 77 Example 2-18 NCOP 0.1 76 80 74 Example2-19 DNCO 0.5 79 85 74 Example 2-20 DNCOB 0.5 80 82 78 Example 2-21 NEP0.5 78 84 79 Example 2-22 NPP 0.5 77 81 79 Example 2-23 NCHP 0.5 77 8177 Example 2-24 NPhP 0.5 78 83 79 Example 2-25 — — C₄F₉OCH₃ 78 82 75Example 2-26 — — C₆F₁₃OCH₃ 77 80 76 Example 2-27 Formula 1 — — — 71 7454 (2-1) Example 2-28 Formula 1 70 74 53 (2-2)

As illustrated in Table 3, in the secondary battery using the artificialgraphite as an anode active material, results similar to the results ofTable 1 and Table 2 were obtained even if the type of the sulfonecompound was changed. That is, in Examples 2-1 to 2-26 in which thecombination of the sulfone compound and the nitrile compound or the likewas used, the discharge capacity retention ratios at 23 deg C. and 45deg C. were higher and safety valve operation time was longer than inExamples 1-33 to 1-49, 2-27, and 2-28 in which the combination of thesulfone compound and the nitrile compound or the like was not used.

Accordingly, it was confirmed that in the secondary battery using theartificial graphite as an anode active material, in the case where thesolvent of the electrolyte contained the sulfone compound and thenitrile compound or the like, cycle characteristics and safety wereimproved.

Examples 3-1 to 3-9

A procedure similar to that of Examples 1-14, 1-19, 1-21, 1-25, 2-1,2-6, 2-8, 2-12, and 1-33 was executed, except that the composition ofthe solvent was changed as illustrated in Table 4. In this case, as asolvent, 4-fluoro-1,3-dioxolane-2-one (FEC) as a halogenated cyclicester carbonate shown in Formula (7) was further used. However, inExamples 3-1 to 3-3, 3-5 to 3-7, and 3-9 in which the ether compound wasnot used, a mixed solvent was prepared so that the composition of EC,DMC, and FEC was 27:70:3 at a weight ratio (EC:DMC:FEC). Further, inExamples 3-4 and 3-8 in which the ether compound was used, a mixedsolvent was prepared so that the composition of EC, DMC, the ethercompound and FEC was 27:60:10:3 at a weight ratio (EC:DMC:ethercompound:FEC). For the secondary batteries of Examples 3-1 to 3-9, cyclecharacteristics respectively at 23 deg C. and 45 deg C. and safety wereexamined The results illustrated in Table 4 were obtained.

TABLE 4 Anode active material: artificial graphite Solvent: EC + DMC +FEC Electrolyte salt: LiPF₆ Other solvent Safety Nitrile compound Cycledischarge valve Sulfone compound or the like capacity retentionoperation Content Content Ether ratio (%) time Type (wt %) Type (wt %)compound 23 deg C. 45 deg C. (time) Example 3-1 Formula 1 SCN 0.1 — 9395 83 Example 3-2 (1-2) DNCO 0.5 92 94 84 Example 3-3 NEP 0.5 91 95 85Example 3-4 — — C₄F₉OCH₃ 89 94 83 Example 3-5 Formula 1 SCN 0.1 — 90 9481 Example 3-6 (2-1) DNCO 0.5 91 93 81 Example 3-7 NEP 0.5 90 91 83Example 3-8 — — C₄F₉OCH₃ 88 94 82 Example 3-9 — — — — — 70 73 53

As illustrated in Table 4, in the secondary battery using the artificialgraphite as an anode active material, results similar to the resultsshown in Table 1 to Table 3 were obtained even if FEC was added to theelectrolyte. That is, in Examples 3-1 to 3-8 in which the combination ofthe sulfone compound and the nitrile compound or the like was used, thecycle discharge capacity retention ratios at 23 deg C. and 45 deg C.were higher and safety valve operation time was longer than in Example3-9 in which the combination of the sulfone compound and the nitrilecompound or the like was not used. In this case, in Examples 3-1 to 3-8,the cycle discharge capacity retention ratios at 23 deg C. and 45 deg C.were higher and safety valve operation time was longer than in Examples1-14, 1-19, 1-21, 1-25, 2-1, 2-6, 2-8, and 2-12 in which FEC was notused. Accordingly, it was confirmed that in the secondary battery usingthe artificial graphite as an anode active material, in the case wherethe solvent of the electrolytic solution contained the sulfone compoundand the nitrile compound or the like, cycle characteristics and safetywere improved even if the composition of the solvent was changed. Inthis case, in particular, it was confirmed that in the case where thesolvent contained the halogenated cyclic ester carbonate shown inFormula (7), cycle characteristics and safety were more improved.

Examples 4-1 to 4-20

A procedure similar to that of Examples 1-14, 1-19, 1-21, 1-25, and 1-33was executed, except that the composition of the solvent was changed asillustrated in Table 5. In this case, as a solvent,trans-4,5-difluoro-1,3-dioxolane-2-one (tDFEC) as the halogenated cyclicester carbonate shown in Formula (7) or vinylene carbonate (VC) as theunsaturated carbon bond cyclic ester carbonate shown in Formula (8) wasused. Further, propene sultone (PRS) as sultone or succinic anhydride(SCAH) as an acid anhydride was used. The content of tDFEC and the likein the solvent was 1 wt %. For the secondary batteries of Examples 4-1to 4-20, cycle characteristics respectively at 23 deg C. and 45 deg C.and safety were examined. The results illustrated in Table 5 wereobtained.

TABLE 5 Anode active material: artificial graphite Solvent: EC + DMCElectrolyte salt: LiPF₆ Cycle Other solvent discharge Nitrile capacitySafety Sulfone compound retention valve compound or the like ratio (%)operation Content Content Ether 23 45 time Solvent Type (wt %) Type (wt%) compound deg C. deg C. (time) Example 4-1 tDFEC Formula 1 SCN 0.1 —91 93 86 Example 4-2 VC (1-2) 90 92 87 Example 4-3 PRS 89 91 87 Example4-4 SCAH 89 90 86 Example 4-5 tDFEC Formula 1 DNCO 0.5 — 90 92 86Example 4-6 VC (1-2) 89 91 86 Example 4-7 PRS 88 88 85 Example 4-8 SCAH90 88 86 Example 4-9 tDFEC Formula 1 NEP 0.5 — 91 93 87 Example 4-10 VC(1-2) 90 91 85 Example 4-11 PRS 89 90 85 Example 4-12 SCAH 90 92 86Example 4-13 tDFEC Formula 1 — — C₄F₉OCH₃ 90 92 86 Example 4-14 VC (1-2)89 91 85 Example 4-15 PRS 89 90 89 Example 4-16 SCAH 88 91 86 Example4-17 tDFEC — — — — — 71 73 53 Example 4-18 VC 66 72 55 Example 4-19 PRS63 66 56 Example 4-20 SCAH 67 71 54

As illustrated in Table 5, in the secondary battery using the artificialgraphite as an anode active material, results similar to the resultsshown in Table 1 and Table 2 were obtained even if tDFEC or the like wasadded to the electrolyte. That is, in Examples 4-1 to 4-16 in which thecombination of the sulfone compound and the nitrile compound or the likewas used, the cycle discharge capacity retention ratios at 23 deg C. and45 deg C. were higher and safety valve operation time was longer than inExamples 4-17 to 4-20 in which the combination of the sulfone compoundand the nitrile compound or the like was not used. In this case, inExamples 4-1 to 4-16 in which tDFEC or the like was used, the cycledischarge capacity retention ratios at 23 deg C. and 45 deg C. andsafety valve operation time were significantly higher than in Examples1-14, 1-19, 1-21, and 1-25 in which tDFEC or the like was not used.Accordingly, it was confirmed that in the secondary battery using theartificial graphite as an anode active material, in the case where thesolvent of the electrolyte contained the sulfone compound and thenitrile compound or the like, cycle characteristics and safety wereimproved even if the composition of the solvent was changed. In thiscase, in particular, it was confirmed that in the case where the solventof the electrolytic solution contained at least one kind of thehalogenated cyclic ester carbonate shown in Formula (7), the unsaturatedcarbon bond cyclic ester carbonate shown in Formula (8), sultone, andthe acid anhydride, cycle characteristics and safety were more improved.

Examples 5-1 to 5-15

A procedure similar to that of Examples 1-14, 1-19, 1-21, 1-25, and 1-33was executed, except that the type of electrolyte salt was changed asillustrated in Table 6 and Table 7. In this case, lithiumtetrafluoroborate (LiBF₄), the compound shown in Formula (11-6) as thecompound shown in Formula (11), or lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI) as the compound shown inFormula (14) was used. At this time, the content of LiPF₆ to the mixedsolvent was 1.1 mol/kg, and the content of LiBF₄ or the like to themixed solvent was 0.1 mol/kg. For the secondary batteries of Examples5-1 to 5-15, cycle characteristics respectively at 23 deg C. and 45 degC., safety, and storage characteristics at 80 deg C. were examined. Theresults illustrated in Table 6 and Table 7 were obtained. In Table 6 andTable 7, the storage characteristics results for the secondary batteriesof Examples 1-14, 1-19, 1-21, 1-25, and 1-33 were also shown.

In examining the storage characteristics, first, 2 cycles of charge anddischarge were performed in the atmosphere at 23 deg C., and thedischarge capacity before storage was measured. Subsequently, after thebattery that had been charged again was stored in a constant temperaturebath at 80 deg C. for 10 days, discharge was performed in the atmosphereat 23 deg C., and the discharge capacity after storage was measured.Finally, the storage discharge capacity retention ratio (%)=(dischargecapacity after storage/discharge capacity before storage)*100 wascalculated. The charge and discharge conditions were similar to those inthe case of examining cycle characteristics.

TABLE 6 Anode active material: artificial graphite; Solvent: EC + DMC;Electrolyte salt: LiPF₆ Cycle discharge capacity Other solvent retentionSafety Storage Sulfone Nitrile compound ratio (%) valve dischargecompound or the like 23 45 operation capacity Content Content EtherElectrolyte deg deg time retention Type (wt %) Type (wt %) compound saltC. C. (time) ratio (%) Example 1-14 Formula 1 SCN 0.1 — — 85 88 80 75Example 5-1 (1-2) LiBF₄ 86 88 92 80 Example 5-2 Formula 85 89 91 81(11-6) Example 5-3 LiTFSI 86 88 92 80 Example 1-19 Formula 1 DNCO 0.5 —— 83 85 81 76 Example 5-4 (1-2) LiBF₄ 85 86 89 81 Example 5-5 Formula 8485 91 82 (11-6) Example 5-6 LiTFSI 83 86 90 80 Example 1-21 Formula 1NEP 0.5 — — 84 88 82 76 Example 5-7 (1-2) LiBF₄ 85 88 88 80 Example 5-8Formula 85 88 89 80 (11-6) Example 5-9 LiTFSI 84 89 89 82 Example 1-25Formula 1 — — C₄F₉OCH₃ — 80 86 81 77 Example 5-10 (1-2) LiBF₄ 81 87 8782 Example 5-11 Formula 81 86 87 80 (11-6) Example 5-12 LiTFSI 80 87 8881

TABLE 7 Anode active material: artificial graphite; Solvent: EC + DMC;Electrolyte salt: LiPF₆ Cycle discharge Other solvent capacity Nitrileretention Safety Storage Sulfone compound ratio (%) valve dischargecompound or the like 23 45 operation capacity Content Content EtherElectrolyte deg deg time retention Type (wt %) Type (wt %) compound saltC. C. (time) ratio (%) Example 1-33 — — — — — — 61 63 54 60 Example 5-13LiBF₄ 57 60 60 68 Example 5-14 Formula 59 62 62 67 (11-6) Example 5-15LiTFSI 60 63 58 69

As illustrated in Table 6 and Table 7, in the secondary battery usingthe artificial graphite as an anode active material, results similar tothe results shown in Table 1 and Table 3 were obtained even if LiBF₄ orthe like was added to the electrolyte. That is, in Examples 5-1 to 5-12in which the combination of the sulfone compound and the nitrilecompound or the like was used, the cycle discharge capacity retentionratios at 23 deg C. and 45 deg C. were higher and safety valve operationtime was longer than in Examples 5-13 to 5-15 in which the combinationof the sulfone compound and the nitrile compound or the like was notused. Further, in this case, in Examples 5-1 to 5-12, the storagedischarge capacity retention ratios were higher than those in Examples5-13 to 5-15. In particular, in Examples 5-1 to 5-12 in which LiBF₄ orthe like was added to the electrolyte, safety valve operation time waslonger and the storage discharge capacity retention ratios weresignificantly higher than in Examples 1-14, 1-19, 1-21, and 1-25 inwhich LiBF₄ or the like was not added to the electrolyte. Accordingly,it was confirmed that in the secondary battery using the artificialgraphite as an anode active material, in the case where the solvent ofthe electrolytic solution contained the sulfone compound and the nitrilecompound or the like, cycle characteristics and safety were improvedeven if the composition of the electrolyte salt was changed. In thiscase, in particular, it was confirmed that in the case where theelectrolyte salt contained at least one kind of LiBF₄, the compoundshown in Formula (11), and the compound shown in Formula (14), safetyand storage characteristics together with cycle characteristics wereimproved.

Examples 6-1 to 6-48

A procedure similar to that of Examples 1-1 to 1-48 was executed, exceptthat the anode 22 was formed by using silicon as an anode activematerial and diethyl carbonate (DEC) was used instead of DMC as asolvent as illustrated in Table 8 and Table 9. In forming the anode 22,silicon was deposited on the surface of the anode current collector 22Amade of an electrolytic copper foil (thickness: 15 μm) by usingevaporation method (electron beam evaporation method), and thereby theanode active material layer 22B containing a plurality of anode activematerial particles was formed. In this case, the total thickness of theanode active material layer 22B was 6 μm. For the secondary batteries ofExamples 6-1 to 6-49, cycle characteristics respectively at 23 deg C.and 45 deg C. and safety were examined. The results illustrated in Table8 and Table 9 were obtained.

TABLE 8 Anode active material: silicon Solvent: EC + DEC Electrolytesalt: LiPF₆ Other solvent Safety Sulfone Nitrile compound Cycledischarge valve compound or the like capacity retention operationContent Content Ether ratio (%) time Type (wt %) Type (wt %) compound 23deg C. 45 deg C. (time) Example 6-1 Formula 1 SCN 0.1 — 61 64 60 Example6-2 (1-1) DCNH 0.1 58 62 59 Example 6-3 PTCN 0.1 57 60 58 Example 6-4TCNQ 0.1 55 61 59 Example 6-5 NCOP 0.1 59 61 59 Example 6-6 DNCO 0.5 6162 61 Example 6-7 DNCOB 0.5 60 61 60 Example 6-8 NEP 0.5 59 62 62Example 6-9 NPP 0.5 59 60 59 Example 6-10 NCHP 0.5 59 61 58 Example 6-11NPhP 0.5 57 60 60 Example 6-12 — — C₄F₉OCH₃ 59 61 61 Example 6-13 — —C₆F₁₃OCH₃ 57 61 60 Example 6-14 Formula 1 SCN 0.1 — 58 61 62 Example6-15 (1-2) DCNH 0.1 55 61 77 Example 6-16 PTCN 0.1 58 59 58 Example 6-17TCNQ 0.1 57 60 78 Example 6-18 NCOP 0.1 58 60 60 Example 6-19 DNCO 0.556 60 63 Example 6-20 DNCOB 0.5 59 60 59 Example 6-21 NEP 0.5 60 63 64Example 6-22 NPP 0.5 57 61 58 Example 6-23 NCHP 0.5 58 60 57 Example6-24 NPhP 0.5 56 59 59 Example 6-25 — — C₄F₉OCH₃ 58 60 61 Example 6-26 —— C₆F₁₃OCH₃ 60 61 60

TABLE 9 Anode active material: silicon Solvent: EC + DEC Electrolytesalt: LiPF₆ Other solvent Cycle discharge Safety Sulfone Nitrilecompound capacity valve compound or the like retention operation ContentContent Ether ratio (%) time Type (wt %) Type (wt %) compound 23 deg C.45 deg C. (time) Example 6-27 Formula 1 SCN + DNCO 0.1 + 0.5 — 67 68 69Example 6-28 (1-2) SCN + NEP 0.1 + 0.5 68 68 68 Example 6-29 DNCO + NEP0.5 + 0.5 68 69 68 Example 6-30 SCN 0.1 C₄F₉OCH₃ 67 68 69 Example 6-31DNCO 0.5 66 67 69 Example 6-32 NEP 0.5 67 69 67 Example 6-33 — — — — —30 32 25 Example 6-34 Formula 1 — — 35 39 30 (1-1) Example 6-35 Formula1 32 35 26 (1-2) Example 6-36 — — SCN 0.1 — 20 21 40 Example 6-37 DCNH0.1 14 16 42 Example 6-38 PTCN 0.1 15 14 40 Example 6-39 TCNQ 0.1 15 1538 Example 6-40 NCOP 0.1 18 19 41 Example 6-41 DNCO 0.5 22 23 42 Example6-42 DNCOB 0.5 19 17 40 Example 6-43 NEP 0.5 19 20 41 Example 6-44 NPP0.5 19 19 40 Example 6-45 NCHP 0.5 19 18 40 Example 6-46 NPhP 0.5 18 1941 Example 6-47 — — C₄F₉OCH₃ 10 11 40 Example 6-48 — — C₆F₁₃OCH₃ 11 1141

As illustrated in Table 8 and Table 9, in the case of using silicon asan anode active material, results similar to the results shown in Table1 and Table 2 were obtained as well. That is, in Examples 6-1 to 6-32 inwhich the combination of the sulfone compound and the nitrile compoundor the like was used, the cycle discharge capacity retention ratios at23 deg C. and 45 deg C. were higher and safety valve operation time waslonger than in Examples 6-33 to 6-48 in which the combination of thesulfone compound and the nitrile compound or the like was not used.Further, in this case, the cycle discharge capacity retention ratio andsafety valve operation time at 23 deg C. and 45 deg C. became favorablewithout depending on the type of the sulfone compound and the type ofthe nitrile compound or the like. Specially, in the case where theplurality of kinds of nitrile compounds were used together with thesulfone compound (Examples 6-27 to 6-32), the cycle discharge capacityretention ratio at 23 deg C. and 45 deg C. and safety valve operationtime became more favorable than in the case that one kind of nitrilecompounds was used (Examples 6-14 to 6-26). Accordingly, it wasconfirmed that in the secondary battery using silicon as an anode activematerial, in the case where the solvent of the electrolyte contained thesulfone compound and the nitrile compound or the like, cyclecharacteristics and safety were improved as well.

Examples 7-1 to 7-28

A procedure similar to that of Examples 2-1 to 2-28 was executed, exceptthat silicon was used as an anode active material and diethyl carbonate(DEC) was used instead of DMC as a solvent as in Examples 6-1 to 6-48 asillustrated in Table 10. For the secondary batteries of Examples 7-1 to7-28, cycle characteristics at 23 deg C. and 45 deg C. and safety valveoperation time were examined. The results illustrated in Table 10 wereobtained.

TABLE 10 Anode active material: silicon Solvent: EC + DEC Electrolytesalt: LiPF₆ Other solvent Cycle discharge Safety Sulfone Nitrilecompound capacity valve compound or the like retention operation ContentContent Ether ratio (%) time Type (wt %) Type (wt %) compound 23 deg C.45 deg C. (time) Example 7-1 Formula 1 SCN 0.1 — 64 67 62 Example 7-2(2-1) DCNH 0.1 61 63 59 Example 7-3 PTCN 0.1 61 65 61 Example 7-4 TCNQ0.1 60 62 60 Example 7-5 NCOP 0.1 62 64 61 Example 7-6 DNCO 0.5 63 65 63Example 7-7 DNCOB 0.5 63 64 62 Example 7-8 NEP 0.5 62 65 64 Example 7-9NPP 0.5 62 63 62 Example 7-10 NCHP 0.5 62 64 61 Example 7-11 NPhP 0.5 6063 62 Example 7-12 — — C₄F₉OCH₃ 62 64 61 Example 7-13 — — C₆F₁₃OCH₃ 6064 62 Example 7-14 Formula 1 SCN 0.1 — 63 66 61 Example 7-15 (2-2) DCNH0.1 59 59 60 Example 7-16 PTCN 0.1 60 64 60 Example 7-17 TCNQ 0.1 58 5961 Example 7-18 NCOP 0.1 61 63 61 Example 7-19 DNCO 0.5 62 64 62 Example7-20 DNCOB 0.5 62 63 61 Example 7-21 NEP 0.5 61 64 63 Example 7-22 NPP0.5 61 62 61 Example 7-23 NCHP 0.5 61 63 61 Example 7-24 NPhP 0.5 59 6260 Example 7-25 — — C₄F₉OCH₃ 61 63 60 Example 7-26 — — C₆F₁₃OCH₃ 59 6361 Example 7-27 Formula 1 — — — 37 40 32 (2-1) Example 7-28 Formula 1 3338 31 (2-2)

As illustrated in Table 10, in the secondary battery using silicon as ananode active material, results similar to the results shown in Table 8and Table 9 were obtained as well even if the type of sulfone compoundwas changed. That is, in Examples 7-1 to 7-26 in which the combinationof the sulfone compound and the nitrile compound or the like was used,the cycle discharge capacity retention ratios at 23 deg C. and 45 deg C.were higher and safety valve operation time was longer than in Examples6-33 to 6-48, 7-27, and 7-28 in which the combination of the sulfonecompound and the nitrile compound or the like was not used. Accordingly,it was confirmed that in the secondary battery using silicon as an anodeactive material, in the case where the solvent of the electrolytecontained the sulfone compound and the nitrile compound or the like,cycle characteristics and safety were improved as well.

Examples 8-1 to 8-9

A procedure similar to that of Examples 3-1 to 3-9 was executed, exceptthat silicon was used as an anode active material and diethyl carbonate(DEC) was used instead of DMC as a solvent as in Examples 6-1 to 6-48 asillustrated in Table 11. For the secondary batteries of Examples 8-1 to8-9, cycle characteristics respectively at 23 deg C. and 45 deg C. andsafety were examined The results illustrated in Table 11 were obtained.

TABLE 11 Anode active material: silicon Solvent: EC + DEC + FECElectrolyte salt: LiPF₆ Other solvent Safety Sulfone Nitrile compoundCycle discharge valve compound or the like capacity retention operationContent Content Ether ratio (%) time Type (wt %) Type (wt %) compound 23deg C. 45 deg C. (time) Example 8-1 Formula 1 SCN 0.1 — 70 74 81 Example8-2 (1-2) DNCO 0.5 71 73 81 Example 8-3 NEP 0.5 70 71 83 Example 8-4 — —C₄F₉OCH₃ 68 74 82 Example 8-5 Formula 1 SCN 0.1 — 73 75 83 Example 8-6(2-1) DNCO 0.5 72 74 84 Example 8-7 NEP 0.5 71 75 85 Example 8-8 — —C₄F₉OCH₃ 69 74 83 Example 8-9 — — — — — 44 47 29

As illustrated in Table 11, in the secondary battery using silicon as ananode active material, results similar to the results shown in Table 6and Table 7 were obtained even if FEC was added to the electrolyte. Thatis, in Examples 8-1 to 8-8 in which the combination of the sulfonecompound and the nitrile compound or the like was used, the dischargecapacity retention ratios at 23 deg C. and 45 deg C. were higher andsafety valve operation time was longer than in Example 8-9 in which thecombination of the sulfone compound and the nitrile compound or the likewas not used. In this case, in Examples 8-1 to 8-8, the cycle dischargecapacity retention ratios at 23 deg C. and 45 deg C. were higher andsafety valve operation time was longer than in Examples 6-14, 6-19,6-21, 6-25, 7-1, 7-6, 7-8, and 7-12 in which FEC was not used.Accordingly, it was confirmed that in the secondary battery usingsilicon as an anode active material, in the case where the solvent ofthe electrolytic solution contained the sulfone compound and the nitrilecompound or the like, cycle characteristics and safety were improvedeven if the composition of the solvent was changed. In this case, inparticular, it was confirmed that in the case where the solventcontained the halogenated cyclic ester carbonate shown in Formula (7),cycle characteristics and safety were more improved.

Examples 9-1 to 9-20

A procedure similar to that of Examples 4-1 to 4-20 was executed, exceptthat silicon was used as an anode active material and diethyl carbonate(DEC) was used instead of DMC as a solvent as in Examples 6-1 to 6-48 asillustrated in Table 12. For the secondary batteries of Examples 9-1 to9-20, cycle characteristics respectively at 23 deg C. and 45 deg C. andsafety were examined The results illustrated in Table 12 were obtained.

TABLE 12 Anode active material: silicon Solvent: EC + DEC Electrolytesalt: LiPF₆ Cycle discharge Other solvent capacity Nitrile retentionSafety Sulfone compound ratio (%) valve compound or the like 23 45operation Content Content Ether deg deg time Solvent Type (wt %) Type(wt %) compound C. C. (time) Example 9-1 tDFEC Formula 1 SCN 0.1 — 72 7480 Example 9-2 VC (1-2) 66 70 83 Example 9-3 PRS 68 70 82 Example 9-4SCAH 67 71 84 Example 9-5 tDFEC Formula 1 DNCO 0.5 — 71 73 80 Example9-6 VC (1-2) 65 68 84 Example 9-7 PRS 67 70 81 Example 9-8 SCAH 65 68 84Example 9-9 tDFEC Formula 1 NEP 0.5 — 70 73 81 Example 9-10 VC (1-2) 6466 84 Example 9-11 PRS 67 71 81 Example 9-12 SCAH 66 68 85 Example 9-13tDFEC Formula 1 — — C₄F₉OCH₃ 67 72 80 Example 9-14 VC (1-2) 65 67 83Example 9-15 PRS 68 70 81 Example 9-16 SCAH 66 68 84 Example 9-17 tDFEC— — — — — 46 48 28 Example 9-18 VC 40 42 26 Example 9-19 PRS 42 43 29Example 9-20 SCAH 41 43 27

As illustrated in Table 12, in the secondary battery using silicon as ananode active material, results similar to the results shown in Table 6and Table 7 were obtained even if tDFEC or the like was added to theelectrolyte. That is, in Examples 9-1 to 9-16 in which the combinationof the sulfone compound and the nitrile compound or the like was used,the cycle discharge capacity retention ratios at 23 deg C. and 45 deg C.were higher and safety valve operation time was longer than in Examples9-1 to 9-20 in which the combination of the sulfone compound and thenitrile compound or the like was not used. In this case, in Examples 9-1to 9-16 in which tDFEC or the like was used, the discharge capacityretention ratios at 23 deg C. and 45 deg C. and safety valve operationtime were significantly higher than in Examples 6-14, 6-19, 6-21, and6-25 in which tDFEC or the like was not used. Accordingly, it wasconfirmed that in the secondary battery using silicon as an anode activematerial, in the case where the solvent of the electrolyte contained thesulfone compound and the nitrile compound or the like, cyclecharacteristics and safety were improved even if the composition of thesolvent was changed. In this case, in particular, it was confirmed thatin the case where the solvent of the electrolytic solution contained atleast one kind of the halogenated cyclic ester carbonate shown inFormula (7), the unsaturated carbon bond cyclic ester carbonate shown inFormula (8), sultone, and the acid anhydride, cycle characteristics andsafety were more improved.

Examples 10-1 to 10-15

A procedure similar to that of Examples 5-1 to 5-15 was executed, exceptthat silicon was used as an anode active material and diethyl carbonate(DEC) was used instead of DMC as a solvent as in Examples 6-1 to 6-48 asillustrated in Table 13 and Table 14. For the secondary batteries ofExamples 10-1 to 10-15, cycle characteristics respectively at 23 deg C.and 45 deg C., safety, and storage characteristics were examined. Theresults illustrated in Table 13 and Table 14 were obtained. In Table 13and Table 14, the storage characteristics results for the secondarybatteries of Examples 6-14, 6-19, 6-21, 6-25, and 6-33 were also shown.

TABLE 13 Anode active material: silicon; Solvent: EC + DEC; Electrolytesalt: LiPF₆ Other solvent Safety Storage Sulfone Nitrile compound Cycledischarge valve discharge compound or the like capacity retentionoperation capacity Content Content Ether Electrolyte ratio (%) timeretention Type (wt %) Type (wt %) compound salt 23 deg C. 45 deg C.(time) ratio (%) Example 6-14 Formula 1 SCN 0.1 — — 58 61 62 59 Example10-1 (1-2) LiBF₄ 60 63 70 79 Example 10-2 Formula 61 64 71 76 (11-6)Example 10-3 LiTFSI 60 63 72 73 Example 6-19 Formula 1 DNCO 0.5 — — 5660 63 60 Example 10-4 (1-2) LiBF₄ 57 62 69 70 Example 10-5 Formula 58 6272 79 (11-6) Example 10-6 LiTFSI 61 63 70 73 Example 6-21 Formula 1 NEP0.5 — — 60 63 64 60 Example 10-7 (1-2) LiBF₄ 62 65 69 69 Example 10-8Formula 62 64 68 72 (11-6) Example 10-9 LiTFSI 61 64 70 79 Example 6-25Formula 1 — — C₄F₉OCH₃ — 58 60 61 57 Example 10-10 (1-2) LiBF₄ 59 64 6968 Example 10-11 Formula 60 61 68 70 (11-6) Example 10-12 LiTFSI 62 6371 78

TABLE 14 Anode active material: silicon; Solvent: EC + DEC; Electrolytesalt: LiPF₆ Cycle discharge Other solvent capacity Nitrile retentionSafety Storage Sulfone compound ratio (%) valve discharge compound orthe like 23 45 operation capacity Content Content Ether Electrolyte degdeg time retention Type (wt %) Type (wt %) compound salt C. C. (time)ratio (%) Example 6-33 — — — — — — 30 32 25 40 Example 10-13 LiBF₄ 28 3128 51 Example 10-14 Formula 31 32 29 50 (11-6) Example 10-15 LiTFSI 3031 27 48

As illustrated in Table 13 and Table 14, in the secondary battery usingsilicon as an anode active material, results similar to the resultsshown in Table 6 and Table 7 were obtained even if LiBF₄ or the like wasadded to the electrolyte. That is, in Examples 10-1 to 10-12 in whichthe combination of the sulfone compound and the nitrile compound or thelike was used, the cycle discharge capacity retention ratios at 23 degC. and 45 deg C. were higher and safety valve operation time was longerthan in Examples 10-13 to 10-15 in which the combination of the sulfonecompound and the nitrile compound or the like was not used. Further, inthis case, in Examples 10-1 to 10-12, the storage discharge capacityretention ratios were higher than those in Examples 10-13 to 10-15. Inparticular, in Examples 10-1 to 10-12 in which LiBF₄ or the like wasadded to the electrolyte, the cycle discharge capacity retention ratiosat 23 deg C. and 45 deg C., safety valve operation time, and the storagedischarge capacity retention ratios were significantly higher than thosein Examples 6-14, 6-19, 6-21, and 6-25 in which LiBF₄ or the like wasnot added to the electrolyte. Accordingly, it was confirmed that in thesecondary battery using silicon as an anode active material, in the casewhere the solvent of the electrolyte contained the sulfone compound andthe nitrile compound or the like, cycle characteristics and safety wereimproved even if the composition of the electrolyte salt was changed. Inthis case, in particular, it was confirmed that in the case where theelectrolyte salt contained at least one kind of LiBF₄, the compoundshown in Formula (11), and the compound shown in Formula (14), safetyand storage characteristics together with cycle characteristics weremore improved.

Examples 11-1 to 11-15

A procedure similar to that of Examples 1-14, 1-19, 1-21, 1-25, 2-1,2-6, 2-8, 2-12, 1-33, 1-35, 2-27, 1-36, 1-41, 1-43, and 1-47 wasexecuted, except that the anode 22 was formed by using theSnCoC-containing material as an anode active material.

In forming the anode 22, first, cobalt powder and tin powder werealloyed to obtain cobalt tin alloy powder. After that, the resultant wasadded with carbon powder and dry-mixed. Subsequently, 10 g of theforegoing mixture and about 400 g of a corundum being 9 mm in diameterwere set in a reaction container of a planetary ball mill (manufacturedby Ito Seisakusho Co.). Subsequently, inside of the reaction containerwas substituted with argon atmosphere. After that, 10 minute operationat 250 rpm and 10 minute break were repeated until the total operationtime reached 20 hours. Subsequently, the reaction container was cooleddown to room temperature and the SnCoC-containing material was takenout. After that, the resultant was screened through a 280 mesh sieve toremove coarse grain.

The composition of the obtained SnCoC-containing material was analyzed.The tin content was 49.5 mass %, the cobalt content was 29.7 mass %, thecarbon content was 19.8 mass %, and the ratio of tin and cobalt(Co/(Sn+Co)) was 37.5 mass %. At this time, the tin content and thecobalt content were measured by Inductively Coupled Plasma (ICP)emission analysis, and the carbon content was measured by carbon sulfuranalyzer. Further, the SnCoC-containing material was analyzed by X-raydiffraction method. A diffraction peak having a half-width of 1.0 deg ormore based on diffraction angle of 2θ in the range of 2θ=20 to 50 degwas observed. Further, in the case where the SnCoC-containing materialwas analyzed by XPS, as illustrated in FIG. 9, peak P1 was obtained. Inthe case where the peak P1 was analyzed, peak P2 of the surfacecontamination carbon and peak P3 of Cls in the SnCoC-containing materialexisting on the lower energy side (region lower than 284.5 eV) wereobtained. From the result, it was confirmed that carbon in theSnCoC-containing material was bonded to other element.

After the SnCoC-containing material was obtained, 80 parts by mass ofthe SnCoC-containing material as an anode active material, 8 parts bymass of polyvinylidene fluoride as an anode binder, and 12 parts by massof graphite as an anode electrical conductor were mixed to obtain ananode mixture. Subsequently, the anode mixture was dispersed inN-methyl-2-pyrrolidone to obtain paste anode mixture slurry. Finally,both faces of the anode current collector 22A made of a copper foil(thickness: 15 μm) were uniformly coated with the anode mixture slurryby using a coating device and the resultant was dried to form the anodeactive material layer 22B (single face thickness: 50 μm). After that,the resultant was compression-molded by using a rolling press machine.

For the secondary batteries of Examples 11-1 to 11-15, cyclecharacteristics respectively at 23 deg C. and 45 deg C. and safety wereexamined. The results illustrated in Table 15 were obtained.

TABLE 15 Anode active material: SnCoC-containing material Solvent: EC +DMC Electrolyte salt: LiPF₆ Other solvent Safety Sulfone Nitrilecompound Cycle discharge valve compound or the like capacity retentionoperation Content Content Ether ratio (%) time Type (wt %) Type (wt %)compound 23 deg C. 45 deg C. (time) Example 11-1 Formula 1 SCN 0.1 — 6870 74 Example 11-2 (1-2) DNCO 0.5 71 73 73 Example 11-3 NEP 0.5 66 70 75Example 11-4 — — C₄F₉OCH₃ 70 72 74 Example 11-5 Formula 1 SCN 0.1 — 7170 72 Example 1-6 (2-1) DNCO 0.5 70 72 71 Example 11-7 NEP 0.5 70 73 69Example 11-8 — — C₄F₉OCH₃ 69 72 73 Example 11-9 — — — — — 43 45 31Example 11-10 Formula 1 — — — 50 52 34 (1-2) Example 11-11 Formula 1 5154 33 (2-1) Example 11-12 — — SCN 0.1 35 36 45 Example 11-13 DNCO 0.5 3636 40 Example 11-14 NEP 0.5 34 35 41 Example 11-15 — — C₄F₉OCH₃ 30 36 42

As illustrated in Table 15, in the case where the SnCoC-containingmaterial was used as an anode active material, results similar to theresults shown in Table 1 to Table 3 and Table 6 to Table 8 were obtainedas well. That is, in Examples 11-1 to 11-8 in which the combination ofthe sulfone compound and the nitrile compound or the like was used, thedischarge capacity retention ratios at 23 deg C. and 45 deg C. werehigher and safety valve operation time was longer than in Examples 11-9to 11-15 in which the combination of the sulfone compound and thenitrile compound or the like was not used. Further, in this case, thedischarge capacity retention ratio and safety valve operation timebecame favorable without depending on the type of the sulfone compoundand the type of the nitrile compound or the like. Accordingly, it wasconfirmed that in the secondary battery using the SnCoC-containingmaterial as an anode active material, in the case where the solvent ofthe electrolyte contained the sulfone compound and the nitrile compoundor the like, cycle characteristics and safety were improved.

Examples 12-1 to 12-10

A procedure similar to that of Examples 11-1 to 11-4 and 11-9 wasexecuted, except that the composition of the solvent was changed asillustrated in Table 16. In this case, as a solvent, FEC or VC was used.In the case where FEC was used, in the examples in which the ethercompound was not used, a mixed solvent was prepared so that thecomposition of EC, DMC, and FEC was 25:70:5 at a weight ratio(EC:DMC:FEC). Further, in the examples in which the ether compound wasused, a mixed solvent was prepared so that the composition of EC, DMC,the ether compound, and FEC was 25:60:10:5 at a weight ratio (EC:DMC:ether compound:FEC). In the case where VC was used, the content thereofin the solvent was 1 wt %. For the secondary batteries of Examples 12-1to 12-10, cycle characteristics and safety respectively at 23 deg C. and45 deg C. were examined. The results illustrated in Table 16 wereobtained.

TABLE 16 Anode active material: SnCoC-containing material Solvent EC +DMC Electrolyte salt: LiPF₆ Cycle discharge Other solvent capacitySafety Sulfone Nitrile compound retention valve compound or the likeratio (%) operation Content Content Ether 23 45 time Solvent Type (wt %)Type (wt %) compound deg C. deg C. (time) Example 12-1 FEC Formula 1 SCN0.1 — 88 91 80 Example 12-2 VC (1-2) 85 85 79 Example 12-3 FEC Formula 1DNCO 0.5 — 89 90 82 Example 12-4 VC (1-2) 86 88 78 Example 12-5 FECFormula 1 NEP 0.5 — 85 85 84 Example 12-6 VC (1-2) 82 84 80 Example 12-7FEC Formula 1 — — C₄F₉OCH₃ 86 88 83 Example 12-8 VC (1-2) 81 84 81Example 12-9 FEC — — — — — 52 55 33 Example 12-10 VC 48 50 34

As illustrated in Table 16, in the secondary battery using theSnCoC-containing material as an anode active material, results similarto the results of Table 15 were obtained even if FEC or the like wasadded to the electrolytic solution. That is, in Examples 12-1 to 12-8 inwhich the combination of the sulfone compound and the nitrile compoundor the like was used, the discharge capacity retention ratios at 23 degC. and 45 deg C. were higher and safety valve operation time was longerthan in Examples 12-9 and 12-10 in which the combination of the sulfonecompound and the nitrile compound or the like was not used. In thiscase, in Examples 12-1 to 12-8 in which FEC or the like was used, thedischarge capacity retention ratios at 23 deg C. and 45 deg C. werehigher and safety valve operation time was longer than in Examples 11-1to 11-4 in which FEC or the like was not used. Accordingly, it wasconfirmed that in the secondary battery using the SnCoC-containingmaterial as an anode active material, in the case where the solvent ofthe electrolyte contained the sulfone compound and the nitrile compoundor the like, cycle characteristics and safety were improved even if thecomposition of the solvent was changed. In this case, in particular, itwas confirmed that in the case where the electrolytic solution containedat least one kind of the halogenated cyclic ester carbonate shown inFormula (7) and the unsaturated carbon bond cyclic ester carbonate shownin Formula (8), cycle characteristics and safety were more improved.

Examples 13-1 to 13-15

A procedure similar to that of Examples 5-3, 5-6, 5-9, 5-12, and 5-15was executed, except that the SnCoC-containing material was used as ananode active material as in Examples 11-1 to 11-15. For the secondarybatteries of Examples 13-1 to 13-5, cycle characteristics and safetyrespectively at 23 deg C. and 45 deg C. were examined. The resultsillustrated in Table 17 were obtained.

TABLE 17 Anode active material: SnCoC-containing material Solvent: EC +DMC Electrolyte salt: LiPF₆ Cycle discharge Other solvent capacitySafety Sulfone Nitrile compound retention valve compound or the likeratio (%) operation Content Content Ether Electrolyte 23 45 time Type(wt %) Type (wt %) compound salt deg C. deg C. (time) Example 13-1Formula 1 SCN 0.1 — LiTFSI 77 81 84 Example 13-2 (1-2) DNCO 0.5 — 79 8082 Example 13-3 NEP 0.5 — 75 77 83 Example 13-4 — — C₄F₉OCH₃ 75 81 82Example 13-5 — — — — — LiTFSI 46 48 33

As illustrated in Table 17, in the secondary battery using theSnCoC-containing material as an anode active material, results similarto the results shown in Table 15 were obtained even if LiTFSI was addedto the electrolyte. That is, in Examples 13-1 to 13-4 in which thecombination of the sulfone compound and the nitrile compound or the likewas used, the cycle discharge capacity retention ratios at 23 deg C. and45 deg C. were higher and safety valve operation time was longer than inExample 13-5 in which the combination of the sulfone compound and thenitrile compound or the like was not used. In particular, in Examples13-1 to 13-4 in which LiTFSI was added to the electrolyte, the cycledischarge capacity retention ratios at 23 deg C. and 45 deg C. werehigher and safety valve operation time was longer than in Examples 11-1to 11-4 in which LiTFSI was not added. Accordingly, it was confirmedthat in the secondary battery using the SnCoC-containing material as ananode active material, in the case where the solvent of the electrolytecontained the sulfone compound and the nitrile compound or the like,cycle characteristics and safety were improved even if the compositionof the electrolyte salt was changed. In this case, in particular, it wasconfirmed that in the case where the electrolyte contained at least onekind of the compounds shown in Formula (14), cycle characteristics andsafety were more improved.

From the foregoing results of Table 1 to Table 17, the following wasconfirmed. That is, in the secondary battery of the present invention,the solvent of the electrolyte contained at least one kind of thesulfone compounds and at least one kind of the nitrile compound, theisocyanate compound, the pyrrolidone compound, and the ether compound.Thereby, cycle characteristics and safety were able to be improvedwithout depending on the type of the anode active material, the solventcomposition, the electrolyte salt composition or the like.

In this case, in the case where the metal material (silicon or theSnCoC-containing material) was used, the increase ratio of the cycledischarge capacity retention ratios at 23 deg C. and 45 deg C. and theincrease ratio of safety valve operation time and the like were largerthan those in the case that the carbon material (artificial graphite)was used as an anode active material. Accordingly, in the case of usingthe metal material as an anode active material, higher effect is able tobe obtained than in the case of using the carbon material. Such a resultmay be obtained for the following reason. That is, in the case where themetal material advantageous to realizing high capacity as an anodeactive material was used, the electrolytic solution was easilydecomposed than in the case of using the carbon material. Accordingly,decomposition inhibition effect of electrolytic solution wassignificantly demonstrated.

The present invention has been described with reference to theembodiment and the examples. However, the present invention is notlimited to the aspects described in the foregoing embodiment and theforegoing examples, and various modifications may be made. For example,use application of the electrolyte of the present invention is notnecessarily limited to the secondary battery, but may be otherelectrochemical device. Examples of other use applications include acapacitor.

Further, in the foregoing embodiment and the foregoing examples, thedescription has been given of the lithium ion secondary battery or thelithium metal secondary battery as a secondary battery type. However,the secondary battery of the present invention is not limited thereto.The present invention is able to be similarly applied to a secondarybattery in which the anode capacity includes the capacity by insertingand extracting lithium ions and the capacity associated withprecipitation and dissolution of lithium metal, and the anode capacityis expressed by the sum of these capacities. In this case, an anodematerial capable of inserting and extracting lithium ions is used as ananode active material. Further, the chargeable capacity of the anodematerial is set to a smaller value than the discharge capacity of thecathode.

Further, in the foregoing embodiment and the foregoing examples, thedescription has been given with the specific examples of the case inwhich the battery structure is the cylindrical type or the laminatedfilm type, and with the specific example in which the battery elementhas the spirally wound structure. However, applicable structures are notlimited thereto. The secondary battery of the present invention is ableto be similarly applied to a battery having other battery structure suchas a square type battery, a coin type battery, and a button type batteryor a battery in which the battery element has other structure such as alaminated structure.

Further, in the foregoing embodiment and the foregoing examples, thoughthe description has been given of the case using lithium as an electrodereactant element, the electrode reactant element is not necessarilylimited thereto. As an electrode reactant, for example, other Group 1element such as sodium (Na) and potassium (K), a Group 2 element such asmagnesium and calcium, or other light metal such as aluminum may beused. The effect of the present invention is able to be obtained withoutdepending on the electrode reactant type, and thus even if the electrodereactant type is changed, similar effect is able to be obtained.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

1. A secondary battery comprising: a cathode; an anode; and anelectrolyte containing a solvent and an electrolyte salt, wherein thesolvent contains at least one type of sulfone compounds expressed byFormula (1) and Formula (2), and at least one of a nitrile compound andcompounds expressed by Formula (3) to Formula (4):

where R1 is an alkylene group with carbon number from 2 to 4 bothinclusive or a halogenated group thereof, an alkenylene group withcarbon number from 2 to 4 both inclusive or a halogenated group thereof,an arylene group or a halogenated group thereof, or a derivativethereof,

where R2 is an alkylene group with carbon number from 2 to 4 bothinclusive or a halogenated group thereof, an alkenylene group withcarbon number from 2 to 4 both inclusive or a halogenated group thereof,an arylene group or a halogenated group thereof, or a derivativethereof,[Chemical Formula 3]R3NCO]_(a)   (3) where R3 is an organic group with “a” valencycontaining carbon (C) and at least one element of oxygen (O), nitrogen(N), sulfur (S), silicon (Si), phosphorus (P), boron (B), and halogen,and where “a” is one of integer numbers from 1 to 3 both inclusive,

where R4 is an alkyl group with carbon number from 2 to 10 bothinclusive, an alkenyl group with carbon number from 2 to 10 bothinclusive, a cycloalkyl group, a cycloalkenyl group, an aromatic ringgroup, a heterocyclic group, or a derivative thereof.
 2. The secondarybattery according to claim 1, wherein the sulfone compound shown in theFormula (1) is one of compounds expressed by Formula (1-1) to Formula(1-22), and the sulfone compound shown in the Formula (2) is one ofcompounds expressed by Formula (2-1) to Formula (2-20):


3. The secondary battery according to claim 2, wherein the sulfonecompound shown in the Formula (1) is the compound expressed by Formula(1-1) or the compound expressed by Formula (1-2), and the sulfonecompound shown in the Formula (2) is the compound expressed by Formula(2-1) or the compound expressed by Formula (2-2).
 4. The secondarybattery according to claim 1, wherein the compound shown in the Formula(3) is 1-isocyanatoethane, 3-isocyanato-1-propene, 2-isocyanatopropane,1-isocyanatopropane, 1-isocyanatobutane, 2-isocyanato-2-methylpropane,2-isocyanatobutane, methylisocyanatoformate, 1-isocyanatopentane,ethylisocyanatoformate, isocyanatobenzene, 1-chloro-3-isocyanatopropane,isocyanatocyclohexane, isocyanatohexane, 1-isocyanatoheptane,diisocyanatomethane, 1,3-diisocyanatopropane, 1,4-diisocyanatobutane,1,6-diisocyanatohexane, 1,8-diisocyanato octane,1,12-diisocyanatododecane, carbonyldiisocyanato,1,4-diisocyanatobutane-1,4-dione, or 1,5-diisocyanatopentane-1,5-dione,and wherein the compound shown in the Formula (4) isN-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone,N-cyclohexyl-2-pyrrolidone, or N-phenyl-2-pyrrolidone.
 5. The secondarybattery according to claim 4, wherein the compound shown in the Formula(3) is 1-isocyanato pentane, 1,8-diisocyanato octane, or1,4-diisocyanato butane-1,4-dione.
 6. The secondary battery according toclaim 1, wherein the solvent contains at least one type of a halogenatedchain ester carbonate expressed by Formula (6), a halogenated cyclicester carbonate expressed by Formula (7), unsaturated carbon bond cyclicester carbonates expressed by Formula (8) to Formula (10), sultone, andan acid anhydride, excluding the sulfone compounds shown in the Formula(1) and the Formula (2),

where R11 to R16 are a hydrogen group, a halogen group, an alkyl group,or a halogenated alkyl group, and where at least one of R11 to R16 isthe halogen group or the halogenated alkyl group,

where R17 to R20 are a hydrogen group, a halogen group, an alkyl group,or a halogenated alkyl group, and where at least one of R17 to R20 isthe halogen group or the halogenated alkyl group,

where R21 and R22 are a hydrogen group or an alkyl group,

where R23 to R26 are a hydrogen group, an alkyl group, a vinyl group, oran aryl group, and where at least one of R23 to R26 is the vinyl groupor the aryl group,

where R27 is an alkylene group.
 7. The secondary battery according toclaim 6, wherein the unsaturated carbon bond cyclic ester carbonate isselected from the group consisting of vinylene carbonate, vinylethylenecarbonate, and methyleneethylene carbonate, wherein the halogenatedchain ester carbonate is selected from the group consisting offluoromethyl methyl carbonate and bis(fluoromethyl) carbonate, whereinthe halogenated cyclic ester carbonate is selected from the groupconsisting of 4-fluoro-1,3-dioxolane-2-one and4,5-difluoro-1,3-dioxolane-2-one, wherein the sultone is selected fromthe group consisting of propane sultone and propene sultone, and whereinthe acid anhydride is selected from the group consisting of succinicanhydride, glutaric anhydride, maleic anhydride, and phthalic anhydride.8. The secondary battery according to claim 1, wherein the electrolytesalt contains at least one type of lithium hexafluorophosphate (LiPF₆),lithium tetrafluoroborate(LiBF₄), lithium perchlorate (LiClO₄), lithiumhexafluoroarsenate (LiAsF₆), and compounds expressed by Formula (11) toFormula (16),

where X31 is a Group 1 element or a Group 2 element in the long periodperiodic table or aluminum (Al), where M31 is a transition metalelement, a Group 13 element, a Group 14 element, or a Group 15 elementin the long period periodic table, where R31 is a halogen group, whereY31 is (O═)C—R32-C(═O)—, —(O═)C—(R33)₂—, or —(O═)C—C(═O)—, where R32 isan alkylene group, a halogenated alkylene group, an arylene group, or ahalogenated arylene group, where R33 is an alkyl group, a halogenatedalkyl group, an aryl group, or a halogenated aryl group, where a3 is oneof integer nubmers 1 to 4, where b3 is 0, 2, or 4, where c3, d3, m3, andn3 are one of integer nubmers 1 to 3,

where X41 is a Group 1 element or a Group 2 element in the long periodperiodic table, where M41 is a transition metal element, a Group 13element, a Group 14 element, or a Group 15 element in the long periodperiodic table, where Y41 is —(O═)C—(C(R41)₂)_(b4)-C—(═O)—,—(R43)₂C—(C(R42)₂)_(c4)-C—(═O)—, —(R43)₂C—(C(R42)₂)_(c4)-C(R43)₂—,—(R43)₂C—(C(R42)₂)_(c4)-S(═O)₂—, —(O═)₂S—(C(R42)₂)_(d4)-S(═O)₂—, or—(O═)C—(C(R42)₂)_(d4)-S—(═O)₂—, where R41 and R43 are a hydrogen group,an alkyl group, a halogen group, or a halogenated alkyl group, where atleast one of R41 and R43 is respectively the halogen group or thehalogenated alkyl group, where R42 is a hydrogen group, an alkyl group,a halogen group, or a halogenated alkyl group, where a4, e4, and n4 are1 or 2, where b4 and d4 are one of integer nubmers 1 to 4, where c4 isone of integer nubmers 0 to 4, and where f4 and m4 are one of integernubmers 1 to 3,

where X51 is a Group 1 element or a Group 2 element in the long periodperiodic table, where M51 is a transition metal element, a Group 13element, a Group 14 element, or a Group 15 element in the long periodperiodic table, where Rf is a fluorinated alkyl group with carbon numberfrom 1 to 10 both inclusive or a fluorinated aryl group with carbonnumber from 1 to 10 both inclusive, where Y51 is—(O═)C—(C(R51)₂)_(d5)-C(═O)—, —(R52)₂C—(C(R51)₂)_(d5)-C(═O)—,—(R52)₂C—(C(R51)₂)_(d5)-C(R52)₂—, —(R52)₂C—(C(R51)₂)_(d5)-S(═O)₂—,—(O═)₂S—(C(R51)₂)_(e5)-(=SO)₂—, or —(O═)C—(C(R51)₂)_(e5)-S(═O)₂—, whereR51 is a hydrogen group, an alkyl group, a halogen group, or ahalogenated alkyl group, where R52 is a hydrogen group, an alkyl group,a halogen group, or a halogenated alkyl group, and at least one thereofis the halogen group or the halogenated alkyl group, and where a5, f5,and n5 are 1 or 2, where b5, c5, and e5 are one of integer nubmers 1 to4, and where d5 is one of integer nubmers 0 to 4, and where g5 and m5are one of integer nubmers 1 to 3LiN(C_(m)F_(2m+1)SO₂)(C_(n)F_(2n+1)SO₂)   (14) where m and n are aninteger number equal to or greater than 1

where R61 is a straight chain or branched perfluoro alkylene group withcarbon number from 2 to 4 both inclusiveLiC(C_(p)F_(2p+1)SO₂)(C_(q)F_(2q+1)SO₂)(C_(r)F_(2r+1)SO₂)   (16) wherep, q, and r are an integer number of 1 or more.
 9. The secondary batteryaccording to claim 8, wherein the compound shown in the Formula (11) isone of compounds expressed by Formula (11-1) to Formula (11-6), whereinthe compound shown in the Formula (12) is one of compounds expressed byFormula (12-1) to Formula (12-8), and wherein the compound shown in theFormula (13) is a compound expressed by Formula (13-1)


10. The secondary battery according to claim 1, wherein the anodecontains a carbon material, lithium metal (Li), or a material that isable to insert and extract an electrode reactant, and wherein the anodefurther contains at least one kind of metal elements and metalloidelements as constituents.
 11. The secondary battery according to claim1, wherein the anode contains a material containing at least one ofsilicon (Si) and tin (Sn) as a constituent element as an anode activematerial.
 12. The secondary battery according to claim 11, wherein thematerial containing at least one of the silicon and the tin as aconstituent element is simple substance of silicon or a materialcontaining tin, cobalt (Co), and carbon (C) as a constituent element,wherein in the material containing tin, cobalt (Co), and carbon (C) as aconstituent element, a carbon content is 9.9 mass % or more and 29.7mass % or less, a ratio of tin and cobalt (Co/(Sn+Co)) is from 20 mass %or more and 70 mass % or less, and half-width of diffraction peakobtained by X-ray diffraction is 1.0 deg or more.
 13. The secondarybattery according to claim 1, wherein the nitrile compound is selectedfrom the group consisting of succinonitrile, 1,6-dicyanohexane,1,2,3-propane tricarbonitrile, and 7,7,8,8-tetracyanoquinodimethane. 14.The secondary battery according to claim 1, wherein the solvent containsat least one of the nitrile compound and the compounds expressed byFormula (3) to Formula (4) in an amount of 0.1% to 0.5% relative to thesolvent.
 15. The secondary battery according to claim 1, wherein the atleast one of the nitrile compound and the compounds expressed by Formula(3) to Formula (4) is selected from the group consisting ofsuccinonitrile, 1,8-dicyanato octane, and N-ethyl-2-pyrrolidone.
 16. Anelectrolyte comprising: a solvent; and an electrolyte salt, wherein thesolvent contains at least one type of sulfone compounds expressed byFormula (1) and Formula (2), and at least one a nitrile compound andcompounds expressed by Formula (3) to Formula (4)

where R1 is an alkylene group with carbon number from 2 to 4 bothinclusive or a halogenated group thereof, an alkenylene group withcarbon number from 2 to 4 both inclusive or a halogenated group thereof,an arylene group or a halogenated group thereof, or a derivativethereof,

where R2 is an alkylene group with carbon number from 2 to 4 bothinclusive or a halogenated group thereof, an alkenylene group withcarbon number from 2 to 4 both inclusive or a halogenated group thereof,an arylene group or a halogenated group thereof, or a derivativethereof,[Chemical Formula 3]R3NCO]_(a)   (3) where R3 is an organic group with “a” valencycontaining carbon and at least one element of oxygen, nitrogen, sulfur,silicon, phosphorus, boron, and halogen, where “a” is one of integernumbers from 1 to 3 both inclusive,

where R4 is an alkyl group with carbon number from 2 to 10 bothinclusive, an alkenyl group with carbon number from 2 to 10 bothinclusive, a cycloalkyl group, a cycloalkenyl group, an aromatic ringgroup, a heterocyclic group, or a derivative thereof.
 17. Theelectrolyte according to claim 16, wherein the sulfone compound shown inthe Formula (1) is the compound expressed by Formula (1-1) or thecompound expressed by Formula (1-2), and the sulfone compound shown inthe Formula (2) is the compound expressed by Formula (2-1) or thecompound expressed by Formula (2-2):


18. The electrolyte according to claim 16, wherein the nitrile compoundis selected from the group consisting of succinonitrile,1,6-dicyanohexane, 1,2,3-propane tricarbonitrile, and7,7,8,8-tetracyanoquinodimethane.
 19. The electrolyte according to claim16, wherein the solvent contains at least one of the nitrile compoundand the compounds expressed by Formula (3) to Formula (4) in an amountof 0.1% to 0.5% relative to the solvent.
 20. The electrolyte accordingto claim 16, wherein the at least one of the nitrile compound and thecompounds expressed by Formula (3) to Formula (4) is selected from thegroup consisting of succinonitrile, 1,8-dicyanato octane, andN-ethyl-2-pyrrolidone.